feat: production readiness improvements

## Error Handling
- Add GlobalErrorBoundary with error classification and recovery
- Add custom error types (SecurityError, ConnectionError, TimeoutError)
- Fix ErrorAlert component syntax errors

## Offline Mode
- Add offlineStore for offline state management
- Implement message queue with localStorage persistence
- Add exponential backoff reconnection (1s→60s)
- Add OfflineIndicator component with status display
- Queue messages when offline, auto-retry on reconnect

## Security Hardening
- Add AES-256-GCM encryption for chat history storage
- Add secure API key storage with OS keychain integration
- Add security audit logging system
- Add XSS prevention and input validation utilities
- Add rate limiting and token generation helpers

## CI/CD (Gitea Actions)
- Add .gitea/workflows/ci.yml for continuous integration
- Add .gitea/workflows/release.yml for release automation
- Support Windows Tauri build and release

## UI Components
- Add LoadingSpinner, LoadingOverlay, LoadingDots components
- Add MessageSkeleton, ConversationListSkeleton skeletons
- Add EmptyMessages, EmptyConversations empty states
- Integrate loading states in ChatArea and ConversationList

## E2E Tests
- Fix WebSocket mock for streaming response tests
- Fix approval endpoint route matching
- Add store state exposure for testing
- All 19 core-features tests now passing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/lib/gateway-client.ts

@@ -87,6 +87,47 @@ export class SecurityError extends Error {
   }
 }
 
+/**
+ * Connection error for WebSocket/HTTP connection failures.
+ */
+export class ConnectionError extends Error {
+  public readonly code?: string;
+  public readonly recoverable: boolean;
+
+  constructor(message: string, code?: string, recoverable: boolean = true) {
+    super(message);
+    this.name = 'ConnectionError';
+    this.code = code;
+    this.recoverable = recoverable;
+  }
+}
+
+/**
+ * Timeout error for request/response timeouts.
+ */
+export class TimeoutError extends Error {
+  public readonly timeout: number;
+
+  constructor(message: string, timeout: number) {
+    super(message);
+    this.name = 'TimeoutError';
+    this.timeout = timeout;
+  }
+}
+
+/**
+ * Authentication error for handshake/token failures.
+ */
+export class AuthenticationError extends Error {
+  public readonly code?: string;
+
+  constructor(message: string, code?: string) {
+    super(message);
+    this.name = 'AuthenticationError';
+    this.code = code;
+  }
+}
+
 /**
  * Validate WebSocket URL security.
  * Ensures non-localhost connections use WSS protocol.