feat(private-service): expose NetBird-only services over tunnel peers

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/manager/api.go

@@ -204,6 +204,7 @@ func (h *handler) getClusters(w http.ResponseWriter, r *http.Request) {
 			SupportsCustomPorts: c.SupportsCustomPorts,
 			RequireSubdomain:    c.RequireSubdomain,
 			SupportsCrowdsec:    c.SupportsCrowdSec,
+			Private:             c.Private,
 		})
 	}
 

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

@@ -208,6 +208,9 @@ func (m *Manager) replaceHostByLookup(ctx context.Context, accountID string, s *
 			target.Host = resource.Domain
 		case service.TargetTypeSubnet:
 			// For subnets we do not do any lookups on the resource
+		case service.TargetTypeCluster:
+			// Cluster targets carry the upstream address on target_id; the
+			// proxy resolves the destination at request time.
 		default:
 			return fmt.Errorf("unknown target type: %s", target.TargetType)
 		}
@@ -779,6 +782,8 @@ func validateTargetReferences(ctx context.Context, transaction store.Store, acco
 			if err := validateResourceTarget(ctx, transaction, accountID, target); err != nil {
 				return err
 			}
+		case service.TargetTypeCluster:
+			// Cluster targets are addressed by target_id; no peer/resource lookup.
 		default:
 			return status.Errorf(status.InvalidArgument, "unknown target type %q for target %q", target.TargetType, target.TargetId)
 		}
@@ -962,12 +967,14 @@ func (m *Manager) ReloadAllServicesForAccount(ctx context.Context, accountID str
 		return fmt.Errorf("failed to get services: %w", err)
 	}
 
+	oidcCfg := m.proxyController.GetOIDCValidationConfig()
+
 	for _, s := range services {
 		err = m.replaceHostByLookup(ctx, accountID, s)
 		if err != nil {
 			return fmt.Errorf("failed to replace host by lookup for service %s: %w", s.ID, err)
 		}
-		m.proxyController.SendServiceUpdateToCluster(ctx, accountID, s.ToProtoMapping(service.Update, "", m.proxyController.GetOIDCValidationConfig()), s.ProxyCluster)
+		m.proxyController.SendServiceUpdateToCluster(ctx, accountID, s.ToProtoMapping(service.Update, "", oidcCfg), s.ProxyCluster)
 	}
 
 	return nil

management/internals/modules/reverseproxy/service/manager/manager_test.go

@@ -1344,3 +1344,40 @@ func TestValidateSubdomainRequirement(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateTargetReferences_ClusterTargetSkipsLookup(t *testing.T) {
+	ctx := context.Background()
+	ctrl := gomock.NewController(t)
+	mockStore := store.NewMockStore(ctrl)
+	accountID := "test-account"
+
+	// No peer or resource lookups must be issued for cluster targets.
+	targets := []*rpservice.Target{
+		{TargetId: "eu.proxy.netbird.io", TargetType: rpservice.TargetTypeCluster},
+	}
+	require.NoError(t, validateTargetReferences(ctx, mockStore, accountID, targets), "cluster target must validate without store lookups")
+}
+
+func TestReplaceHostByLookup_SkipsClusterTarget(t *testing.T) {
+	ctx := context.Background()
+	ctrl := gomock.NewController(t)
+	mockStore := store.NewMockStore(ctrl)
+	accountID := "test-account"
+
+	mgr := &Manager{store: mockStore}
+
+	svc := &rpservice.Service{
+		ID:        "svc-1",
+		AccountID: accountID,
+		Targets: []*rpservice.Target{
+			{
+				TargetId:   "eu.proxy.netbird.io",
+				TargetType: rpservice.TargetTypeCluster,
+				Host:       "127.0.0.1",
+			},
+		},
+	}
+
+	require.NoError(t, mgr.replaceHostByLookup(ctx, accountID, svc), "cluster target must not trigger peer/resource lookup")
+	assert.Equal(t, "127.0.0.1", svc.Targets[0].Host, "operator-supplied host must be preserved for cluster target")
+}