[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.

shared/management/proto/proxy_service_grpc.pb.go

@@ -35,6 +35,14 @@ type ProxyServiceClient interface {
 	// ValidateSession validates a session token and checks user access permissions.
 	// Called by the proxy after receiving a session token from OIDC callback.
 	ValidateSession(ctx context.Context, in *ValidateSessionRequest, opts ...grpc.CallOption) (*ValidateSessionResponse, error)
+	// ValidateTunnelPeer resolves an inbound peer by its WireGuard tunnel IP and
+	// checks the resolved user's access against the service's access_groups.
+	// Acts as a fast-path equivalent of OIDC for requests originating on the
+	// netbird mesh: when the source IP maps to a known peer in the calling
+	// account and that peer is in the service's access_groups, the proxy can
+	// issue a session cookie without redirecting through the OIDC flow.
+	// Mirrors ValidateSession's response shape.
+	ValidateTunnelPeer(ctx context.Context, in *ValidateTunnelPeerRequest, opts ...grpc.CallOption) (*ValidateTunnelPeerResponse, error)
 }
 
 type proxyServiceClient struct {
@@ -162,6 +170,15 @@ func (c *proxyServiceClient) ValidateSession(ctx context.Context, in *ValidateSe
 	return out, nil
 }
 
+func (c *proxyServiceClient) ValidateTunnelPeer(ctx context.Context, in *ValidateTunnelPeerRequest, opts ...grpc.CallOption) (*ValidateTunnelPeerResponse, error) {
+	out := new(ValidateTunnelPeerResponse)
+	err := c.cc.Invoke(ctx, "/management.ProxyService/ValidateTunnelPeer", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 // ProxyServiceServer is the server API for ProxyService service.
 // All implementations must embed UnimplementedProxyServiceServer
 // for forward compatibility
@@ -183,6 +200,14 @@ type ProxyServiceServer interface {
 	// ValidateSession validates a session token and checks user access permissions.
 	// Called by the proxy after receiving a session token from OIDC callback.
 	ValidateSession(context.Context, *ValidateSessionRequest) (*ValidateSessionResponse, error)
+	// ValidateTunnelPeer resolves an inbound peer by its WireGuard tunnel IP and
+	// checks the resolved user's access against the service's access_groups.
+	// Acts as a fast-path equivalent of OIDC for requests originating on the
+	// netbird mesh: when the source IP maps to a known peer in the calling
+	// account and that peer is in the service's access_groups, the proxy can
+	// issue a session cookie without redirecting through the OIDC flow.
+	// Mirrors ValidateSession's response shape.
+	ValidateTunnelPeer(context.Context, *ValidateTunnelPeerRequest) (*ValidateTunnelPeerResponse, error)
 	mustEmbedUnimplementedProxyServiceServer()
 }
 
@@ -214,6 +239,9 @@ func (UnimplementedProxyServiceServer) GetOIDCURL(context.Context, *GetOIDCURLRe
 func (UnimplementedProxyServiceServer) ValidateSession(context.Context, *ValidateSessionRequest) (*ValidateSessionResponse, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method ValidateSession not implemented")
 }
+func (UnimplementedProxyServiceServer) ValidateTunnelPeer(context.Context, *ValidateTunnelPeerRequest) (*ValidateTunnelPeerResponse, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method ValidateTunnelPeer not implemented")
+}
 func (UnimplementedProxyServiceServer) mustEmbedUnimplementedProxyServiceServer() {}
 
 // UnsafeProxyServiceServer may be embedded to opt out of forward compatibility for this service.
@@ -382,6 +410,24 @@ func _ProxyService_ValidateSession_Handler(srv interface{}, ctx context.Context,
 	return interceptor(ctx, in, info, handler)
 }
 
+func _ProxyService_ValidateTunnelPeer_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(ValidateTunnelPeerRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(ProxyServiceServer).ValidateTunnelPeer(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/management.ProxyService/ValidateTunnelPeer",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(ProxyServiceServer).ValidateTunnelPeer(ctx, req.(*ValidateTunnelPeerRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
 // ProxyService_ServiceDesc is the grpc.ServiceDesc for ProxyService service.
 // It's only intended for direct use with grpc.RegisterService,
 // and not to be introspected or modified (even as a copy)
@@ -413,6 +459,10 @@ var ProxyService_ServiceDesc = grpc.ServiceDesc{
 			MethodName: "ValidateSession",
 			Handler:    _ProxyService_ValidateSession_Handler,
 		},
+		{
+			MethodName: "ValidateTunnelPeer",
+			Handler:    _ProxyService_ValidateTunnelPeer_Handler,
+		},
 	},
 	Streams: []grpc.StreamDesc{
 		{