[management, client, proxy] add expose NetBird-only services over tunnel peers (#6226)

Adds a new "private" service mode for the reverse proxy: services reachable exclusively over the embedded WireGuard tunnel, gated by per-peer group membership instead of operator auth schemes.

Wire contract
- ProxyMapping.private (field 13): the proxy MUST call ValidateTunnelPeer and fail closed; operator schemes are bypassed.
- ProxyCapabilities.private (4) + supports_private_service (5): capability gate. Management never streams private mappings to proxies that don't claim the capability; the broadcast path applies the same filter via filterMappingsForProxy.
- ValidateTunnelPeer RPC: resolves an inbound tunnel IP to a peer, checks the peer's groups against service.AccessGroups, and mints a session JWT on success. checkPeerGroupAccess fails closed when a private service has empty AccessGroups.
- ValidateSession/ValidateTunnelPeer responses now carry peer_group_ids + peer_group_names so the proxy can authorise policy-aware middlewares without an extra management round-trip.
- ProxyInboundListener + SendStatusUpdate.inbound_listener: per-account inbound listener state surfaced to dashboards.
- PathTargetOptions.direct_upstream (11): bypass the embedded NetBird client and dial the target via the proxy host's network stack for upstreams reachable without WireGuard.

Data model
- Service.Private (bool) + Service.AccessGroups ([]string, JSON- serialised). Validate() rejects bearer auth on private services. Copy() deep-copies AccessGroups. pgx getServices loads the columns.
- DomainConfig.Private threaded into the proxy auth middleware. Request handler routes private services through forwardWithTunnelPeer and returns 403 on validation failure.
- Account-level SynthesizePrivateServiceZones (synthetic DNS) and injectPrivateServicePolicies (synthetic ACL) gate on len(svc.AccessGroups) > 0.

Proxy
- /netbird proxy --private (embedded mode) flag; Config.Private in proxy/lifecycle.go.
- Per-account inbound listener (proxy/inbound.go) binding HTTP/HTTPS on the embedded NetBird client's WireGuard tunnel netstack.
- proxy/internal/auth/tunnel_cache: ValidateTunnelPeer response cache with single-flight de-duplication and per-account eviction.
- Local peerstore short-circuit: when the inbound IP isn't in the account roster, deny fast without an RPC.
- proxy/server.go reports SupportsPrivateService=true and redacts the full ProxyMapping JSON from info logs (auth_token + header-auth hashed values now only at debug level).

Identity forwarding
- ValidateSessionJWT returns user_id, email, method, groups, group_names. sessionkey.Claims carries Email + Groups + GroupNames so the proxy can stamp identity onto upstream requests without an extra management round-trip on every cookie-bearing request.
- CapturedData carries userEmail / userGroups / userGroupNames; the proxy stamps X-NetBird-User and X-NetBird-Groups on r.Out from the authenticated identity (strips client-supplied values first to prevent spoofing).
- AccessLog.UserGroups: access-log enrichment captures the user's group memberships at write time so the dashboard can render group context without reverse-resolving stale memberships.

OpenAPI/dashboard surface
- ReverseProxyService gains private + access_groups; ReverseProxyCluster gains private + supports_private. ReverseProxyTarget target_type enum gains "cluster". ServiceTargetOptions gains direct_upstream. ProxyAccessLog gains user_groups.

management/internals/modules/reverseproxy/service/service_test.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/netbirdio/netbird/management/internals/modules/reverseproxy/proxy"
 	"github.com/netbirdio/netbird/shared/hash/argon2id"
+	"github.com/netbirdio/netbird/shared/management/http/api"
 	"github.com/netbirdio/netbird/shared/management/proto"
 )
 
@@ -1116,3 +1117,191 @@ func TestValidate_HeaderAuths(t *testing.T) {
 		assert.Contains(t, err.Error(), "exceeds maximum length")
 	})
 }
+
+func TestValidate_HTTPClusterTarget(t *testing.T) {
+	rp := validProxy()
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Host:       "backend.lan",
+		Options:    TargetOptions{DirectUpstream: true},
+		Enabled:    true,
+	}}
+	require.NoError(t, rp.Validate(), "HTTP cluster target with target_id, host, and direct_upstream must validate")
+}
+
+func TestValidate_HTTPClusterTarget_RequiresTargetId(t *testing.T) {
+	rp := validProxy()
+	rp.Targets = []*Target{{
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Host:       "backend.lan",
+		Options:    TargetOptions{DirectUpstream: true},
+		Enabled:    true,
+	}}
+	assert.ErrorContains(t, rp.Validate(), "empty target_id", "cluster target must reject empty target_id")
+}
+
+// TestValidate_HTTPClusterTarget_RequiresHost pins the new cluster-target
+// rule that operator-supplied Host is mandatory: cluster targets dial the
+// upstream via the host network stack (direct_upstream is implied), so an
+// empty Host leaves the proxy with nothing to dial.
+func TestValidate_HTTPClusterTarget_RequiresHost(t *testing.T) {
+	rp := validProxy()
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Options:    TargetOptions{DirectUpstream: true},
+		Enabled:    true,
+	}}
+	assert.ErrorContains(t, rp.Validate(), "empty host", "cluster target must reject empty host")
+}
+
+// TestValidate_HTTPClusterTarget_RequiresDirectUpstream pins the second
+// half of the cluster-target rule: DirectUpstream must be true so the
+// stdlib transport branch in MultiTransport is taken. Without it the
+// embedded NetBird client would try to dial the cluster address through
+// the WG tunnel, which is the wrong network for a cluster upstream.
+func TestValidate_HTTPClusterTarget_RequiresDirectUpstream(t *testing.T) {
+	rp := validProxy()
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Host:       "backend.lan",
+		Enabled:    true,
+	}}
+	assert.ErrorContains(t, rp.Validate(), "direct upstream disabled", "cluster target must reject direct_upstream=false")
+}
+
+func TestValidate_L4ClusterTarget(t *testing.T) {
+	rp := validProxy()
+	rp.Mode = ModeTCP
+	rp.ListenPort = 9000
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "tcp",
+		Enabled:    true,
+	}}
+	require.NoError(t, rp.Validate(), "L4 cluster target must validate without an explicit port")
+}
+
+func TestService_Copy_RoundtripsPrivate(t *testing.T) {
+	svc := validProxy()
+	svc.Private = true
+	svc.AccessGroups = []string{"grp-admins", "grp-ops"}
+	cp := svc.Copy()
+	require.NotNil(t, cp)
+	assert.True(t, cp.Private)
+	assert.Equal(t, []string{"grp-admins", "grp-ops"}, cp.AccessGroups)
+
+	cp.Private = false
+	assert.True(t, svc.Private)
+
+	cp.AccessGroups[0] = "grp-other"
+	assert.Equal(t, []string{"grp-admins", "grp-ops"}, svc.AccessGroups)
+}
+
+func TestService_APIRoundtrip_Private(t *testing.T) {
+	enabled := true
+	private := true
+	accessGroups := []string{"grp-admins"}
+	targets := []api.ServiceTarget{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: api.ServiceTargetTargetType("cluster"),
+		Protocol:   "http",
+		Port:       80,
+		Enabled:    true,
+	}}
+	req := &api.ServiceRequest{
+		Name:         "svc-private",
+		Domain:       "myapp.eu.proxy.netbird.io",
+		Enabled:      enabled,
+		Private:      &private,
+		AccessGroups: &accessGroups,
+		Targets:      &targets,
+	}
+
+	svc := &Service{}
+	require.NoError(t, svc.FromAPIRequest(req, "acc-1"))
+	assert.True(t, svc.Private)
+	assert.Equal(t, []string{"grp-admins"}, svc.AccessGroups)
+
+	resp := svc.ToAPIResponse()
+	require.NotNil(t, resp.Private)
+	assert.True(t, *resp.Private)
+	require.NotNil(t, resp.AccessGroups)
+	assert.Equal(t, []string{"grp-admins"}, *resp.AccessGroups)
+}
+
+func TestValidate_Private_RequiresAccessGroups(t *testing.T) {
+	rp := validProxy()
+	rp.Private = true
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Host:       "backend.lan",
+		Options:    TargetOptions{DirectUpstream: true},
+		Enabled:    true,
+	}}
+	assert.ErrorContains(t, rp.Validate(), "access group")
+}
+
+func TestValidate_Private_RejectsBearerAuth(t *testing.T) {
+	rp := validProxy()
+	rp.Private = true
+	rp.AccessGroups = []string{"grp-admins"}
+	rp.Auth.BearerAuth = &BearerAuthConfig{
+		Enabled:            true,
+		DistributionGroups: []string{"grp-sso"},
+	}
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Host:       "backend.lan",
+		Options:    TargetOptions{DirectUpstream: true},
+		Enabled:    true,
+	}}
+	assert.ErrorContains(t, rp.Validate(), "mutually exclusive")
+}
+
+func TestValidate_Private_AcceptsNonClusterTargets(t *testing.T) {
+	rp := validProxy()
+	rp.Private = true
+	rp.AccessGroups = []string{"grp-admins"}
+	require.NoError(t, rp.Validate())
+}
+
+func TestValidate_Private_AcceptsClusterTargetWithAccessGroups(t *testing.T) {
+	rp := validProxy()
+	rp.Private = true
+	rp.AccessGroups = []string{"grp-admins"}
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "http",
+		Host:       "backend.lan",
+		Options:    TargetOptions{DirectUpstream: true},
+		Enabled:    true,
+	}}
+	require.NoError(t, rp.Validate())
+}
+
+func TestValidate_Private_RejectsNonHTTPMode(t *testing.T) {
+	rp := validProxy()
+	rp.Private = true
+	rp.AccessGroups = []string{"grp-admins"}
+	rp.Mode = ModeTCP
+	rp.Targets = []*Target{{
+		TargetId:   "eu.proxy.netbird.io",
+		TargetType: TargetTypeCluster,
+		Protocol:   "tcp",
+		Enabled:    true,
+	}}
+	assert.ErrorContains(t, rp.Validate(), "HTTP")
+}