fix(desktop): session persistence — refresh/login/context/empty-content 4-bug fix

1. App.tsx: add restoreSession() call on startup to prevent redirect
   to login page after refresh (isRestoring guard + BootstrapScreen)
2. CloneManager: call syncAgents() after loadClones() to restore
   currentAgent and conversation history on app load
3. zclaw-memory: add get_or_create_session() so frontend session UUID
   is persisted directly — kernel no longer creates mismatched IDs
4. openai.rs: assistant message content must be non-empty for
   Kimi/Qwen APIs — replace empty content with meaningful placeholders

Also includes admin-v2 ModelServices unified page (merge providers +
models + API keys into expandable row layout)

desktop/src/components/CloneManager.tsx

@@ -20,7 +20,11 @@ export function CloneManager() {
 
   useEffect(() => {
     if (connected) {
-      loadClones();
+      loadClones().then(() => {
+        // Sync agents in chatStore and restore currentAgent/conversation
+        const clones = useAgentStore.getState().clones;
+        useChatStore.getState().syncAgents(clones);
+      });
     }
   }, [connected, loadClones]);