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)

crates/zclaw-memory/src/store.rs

@@ -173,6 +173,49 @@ impl MemoryStore {
         Ok(session_id)
     }
 
+    /// Get an existing session or create it with the given ID.
+    ///
+    /// This is the critical bridge between frontend session IDs and the database.
+    /// The frontend generates a UUID (`sessionKey`) and sends it with each message.
+    /// Without this method, the kernel would create a *different* session ID on
+    /// every call, so conversation history would never be found.
+    pub async fn get_or_create_session(
+        &self,
+        session_id: &SessionId,
+        agent_id: &AgentId,
+    ) -> Result<SessionId> {
+        let session_str = session_id.to_string();
+        let agent_str = agent_id.to_string();
+
+        // Check if session already exists
+        let exists: bool = sqlx::query_scalar(
+            "SELECT COUNT(*) > 0 FROM sessions WHERE id = ?",
+        )
+        .bind(&session_str)
+        .fetch_one(&self.pool)
+        .await
+        .unwrap_or(false);
+
+        if exists {
+            return Ok(session_id.clone());
+        }
+
+        // Create session with the frontend-provided ID
+        sqlx::query(
+            r#"
+            INSERT INTO sessions (id, agent_id, created_at, updated_at)
+            VALUES (?, ?, datetime('now'), datetime('now'))
+            "#,
+        )
+        .bind(&session_str)
+        .bind(&agent_str)
+        .execute(&self.pool)
+        .await
+        .map_err(|e| ZclawError::StorageError(e.to_string()))?;
+
+        Ok(session_id.clone())
+    }
+
     /// Append a message to a session
     pub async fn append_message(&self, session_id: &SessionId, message: &Message) -> Result<()> {
         let session_str = session_id.to_string();