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-runtime/src/driver/openai.rs

@@ -360,10 +360,14 @@ impl OpenAiDriver {
 
             if let Some(calls) = calls {
                 if !calls.is_empty() {
-                    // Merge assistant content + reasoning into the tool call message
+                    // Merge assistant content + reasoning into the tool call message.
+                    // IMPORTANT: Some APIs (Kimi, Qwen) require `content` to be non-empty
+                    // even when tool_calls is set. Use a meaningful placeholder if content is empty.
+                    let content_value = content.filter(|s| !s.trim().is_empty())
+                        .unwrap_or_else(|| "正在调用工具...".to_string());
                     out.push(OpenAiMessage {
                         role: "assistant".to_string(),
-                        content: content.filter(|s| !s.is_empty()),
+                        content: Some(content_value),
                         reasoning_content: reasoning.filter(|s| !s.is_empty()),
                         tool_calls: Some(calls),
                         tool_call_id: None,
@@ -371,11 +375,14 @@ impl OpenAiDriver {
                     return;
                 }
             }
-            // No tool calls — emit a plain assistant message
+            // No tool calls — emit a plain assistant message.
+            // Ensure content is always Some() and non-empty to satisfy API requirements.
             if content.is_some() || reasoning.is_some() {
+                let content_value = content.filter(|s| !s.trim().is_empty())
+                    .unwrap_or_else(|| "正在思考...".to_string());
                 out.push(OpenAiMessage {
                     role: "assistant".to_string(),
-                    content: content.filter(|s| !s.is_empty()),
+                    content: Some(content_value),
                     reasoning_content: reasoning.filter(|s| !s.is_empty()),
                     tool_calls: None,
                     tool_call_id: None,