[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.

client/internal/dns/server.go

@@ -301,6 +301,11 @@ func newDefaultServer(
 		warningDelayBase:  defaultWarningDelayBase,
 		healthRefresh:     make(chan struct{}, 1),
 	}
+	// Wire the local resolver against the peer status recorder so it can
+	// suppress A/AAAA answers that point at disconnected peers (typical
+	// case: synthesised private-service records pointing at an embedded
+	// proxy peer that just went offline).
+	defaultServer.localResolver.SetPeerConnectivity(localPeerConnectivity{statusRecorder})
 
 	// register with root zone, handler chain takes care of the routing
 	dnsService.RegisterMux(".", handlerChain)
@@ -1386,3 +1391,25 @@ func (s *DefaultServer) PopulateManagementDomain(mgmtURL *url.URL) error {
 	}
 	return nil
 }
+
+// localPeerConnectivity adapts *peer.Status to local.PeerConnectivity so
+// the local resolver can ask "is this IP a known peer and is it
+// connected?" without taking on the peer package as a dependency.
+// A nil status recorder always reports known=false so the resolver
+// short-circuits to the legacy "return everything" path.
+type localPeerConnectivity struct {
+	status *peer.Status
+}
+
+// IsConnectedByIP looks the IP up in the peerstore and surfaces both
+// the known and connected bits. Used by Resolver.filterDisconnectedPeerAnswers.
+func (l localPeerConnectivity) IsConnectedByIP(ip string) (known, connected bool) {
+	if l.status == nil {
+		return false, false
+	}
+	state, ok := l.status.PeerStateByIP(ip)
+	if !ok {
+		return false, false
+	}
+	return true, state.ConnStatus == peer.StatusConnected
+}