[management] Fix agent-network proxy-peer fan-out on affected-peer recompute

The affected-peers resolver loaded only persisted reverse-proxy services, but
agent-network services are synthesized on demand and never persisted. As a
result the embedded proxy peer was never folded into the affected set when a
client's group changed, so the proxy received no network-map update for a newly
authorised client and rejected its handshake until a full resync (restart).

loadProxyServices now merges the synthesized agent-network services (injected
via a registration hook to avoid an import cycle), so proxy peers learn newly
authorised clients immediately.

management/server/agentnetwork/affectedpeers_hook.go

@@ -0,0 +1,15 @@
+package agentnetwork
+
+import "github.com/netbirdio/netbird/management/server/affectedpeers"
+
+// init registers the agent-network service synthesiser with the affectedpeers
+// resolver. Agent-network reverse-proxy services are synthesised on demand and
+// never persisted, so the resolver can't load them from the store; without them
+// it can't fold the embedded proxy peer into the affected set on a client
+// group/peer change, and the proxy never learns a newly authorised client until
+// it reconnects. Registered here (rather than via a direct
+// affectedpeers→agentnetwork import) to avoid an import cycle
+// (agentnetwork → account → affectedpeers).
+func init() {
+	affectedpeers.SetAgentNetworkSynthesizer(SynthesizeServices)
+}