feat: Fix SEO agent behavior and add z.ai API validation

- Add "SEO-First" mode to prevent unwanted agent switching
- SEO agent now stays locked and answers queries through SEO lens
- Add [SUGGEST_AGENT:xxx] marker for smart agent suggestions
- Add suggestion banner UI with Switch/Dismiss buttons
- Prevent auto-switching mid-response

- Add validateConnection() method to ZaiPlanService
- Add debounced API key validation (500ms) in Settings
- Add inline status indicators (valid/validating/error)
- Add persistent validation cache (5min) in localStorage
- Add "Test Connection" button for manual re-validation
- Add clear error messages for auth failures

- Add ApiValidationStatus interface
- Add apiValidationStatus state for tracking connection states
- Add setApiValidationStatus action

- Real-time API key validation in Settings panel
- Visual status indicators (✓/✗/🔄)
- Agent suggestion banner with Switch/Dismiss actions

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

lib/store.ts

@@ -10,6 +10,13 @@ interface AIAssistTab {
   showCanvas?: boolean;
 }
 
+interface ApiValidationStatus {
+  valid: boolean;
+  error?: string;
+  lastValidated?: number;
+  models?: string[];
+}
+
 interface AppState {
   currentPrompt: string;
   enhancedPrompt: string | null;
@@ -29,6 +36,7 @@ interface AppState {
   selectedModels: Record<ModelProvider, string>;
   availableModels: Record<ModelProvider, string[]>;
   apiKeys: Record<ModelProvider, string>;
+  apiValidationStatus: Record<ModelProvider, ApiValidationStatus>;
   qwenTokens?: {
     accessToken: string;
     refreshToken?: string;
@@ -65,6 +73,7 @@ interface AppState {
   setSelectedModel: (provider: ModelProvider, model: string) => void;
   setAvailableModels: (provider: ModelProvider, models: string[]) => void;
   setApiKey: (provider: ModelProvider, key: string) => void;
+  setApiValidationStatus: (provider: ModelProvider, status: ApiValidationStatus) => void;
   setQwenTokens: (tokens?: { accessToken: string; refreshToken?: string; expiresAt?: number } | null) => void;
   setGithubToken: (token: string | null) => void;
   setProcessing: (processing: boolean) => void;
@@ -110,6 +119,11 @@ const useStore = create<AppState>((set) => ({
     zai: "",
   },
   githubToken: null,
+  apiValidationStatus: {
+    qwen: { valid: false },
+    ollama: { valid: false },
+    zai: { valid: false },
+  },
   isProcessing: false,
   error: null,
   history: [],
@@ -176,6 +190,13 @@ const useStore = create<AppState>((set) => ({
     set((state) => ({
       apiKeys: { ...state.apiKeys, [provider]: key },
     })),
+  setApiValidationStatus: (provider, status) =>
+    set((state) => ({
+      apiValidationStatus: {
+        ...state.apiValidationStatus,
+        [provider]: status,
+      },
+    })),
   setQwenTokens: (tokens) => set({ qwenTokens: tokens }),
   setGithubToken: (token) => set({ githubToken: token }),
   setProcessing: (processing) => set({ isProcessing: processing }),