[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/peers/manager.go

@@ -5,6 +5,7 @@ package peers
 import (
 	"context"
 	"fmt"
+	"net"
 	"time"
 
 	"github.com/rs/xid"
@@ -35,6 +36,14 @@ type Manager interface {
 	SetAccountManager(accountManager account.Manager)
 	GetPeerID(ctx context.Context, peerKey string) (string, error)
 	CreateProxyPeer(ctx context.Context, accountID string, peerKey string, cluster string) error
+	// GetPeerByTunnelIP looks up a peer in accountID by its WireGuard tunnel IP.
+	// Returns nil with an error when no match exists. No permission check;
+	// callers (the proxy's ValidateTunnelPeer RPC) are trusted server components.
+	GetPeerByTunnelIP(ctx context.Context, accountID string, ip net.IP) (*peer.Peer, error)
+	// GetPeerWithGroups returns the peer and the list of *types.Group it belongs
+	// to. Used by the proxy's auth path to authorise a request by the calling
+	// peer's group memberships.
+	GetPeerWithGroups(ctx context.Context, accountID, peerID string) (*peer.Peer, []*types.Group, error)
 }
 
 type managerImpl struct {
@@ -99,6 +108,26 @@ func (m *managerImpl) GetPeersByGroupIDs(ctx context.Context, accountID string,
 	return m.store.GetPeersByGroupIDs(ctx, accountID, groupsIDs)
 }
 
+// GetPeerByTunnelIP delegates to the store's indexed lookup.
+func (m *managerImpl) GetPeerByTunnelIP(ctx context.Context, accountID string, ip net.IP) (*peer.Peer, error) {
+	return m.store.GetPeerByIP(ctx, store.LockingStrengthNone, accountID, ip)
+}
+
+// GetPeerWithGroups returns the peer plus its group memberships. Any store
+// error returns (nil, nil, err) so callers never receive a valid peer
+// alongside a non-nil error.
+func (m *managerImpl) GetPeerWithGroups(ctx context.Context, accountID, peerID string) (*peer.Peer, []*types.Group, error) {
+	p, err := m.store.GetPeerByID(ctx, store.LockingStrengthNone, accountID, peerID)
+	if err != nil {
+		return nil, nil, err
+	}
+	groups, err := m.store.GetPeerGroups(ctx, store.LockingStrengthNone, accountID, peerID)
+	if err != nil {
+		return nil, nil, err
+	}
+	return p, groups, nil
+}
+
 func (m *managerImpl) DeletePeers(ctx context.Context, accountID string, peerIDs []string, userID string, checkConnected bool) error {
 	settings, err := m.store.GetAccountSettings(ctx, store.LockingStrengthNone, accountID)
 	if err != nil {