fix(desktop): prevent transformCallback crash in browser mode

Root cause: ChatArea.tsx called listen() from @tauri-apps/api/event
directly on component mount without checking isTauriRuntime(). When
accessed from a regular browser (not Tauri WebView), window.__TAURI_INTERNALS__
is undefined, causing "Cannot read properties of undefined (reading 'transformCallback')".

Solution:
- Created lib/safe-tauri.ts with safe wrappers (safeInvoke, safeListen,
  safeListenEvent, requireInvoke) that gracefully degrade when Tauri
  IPC is unavailable
- Replaced direct listen() call in ChatArea.tsx with safeListenEvent()

desktop/src/components/ChatArea.tsx

@@ -7,7 +7,8 @@ import { useArtifactStore } from '../store/chat/artifactStore';
 import { useConnectionStore } from '../store/connectionStore';
 import { useAgentStore } from '../store/agentStore';
 import { useConfigStore } from '../store/configStore';
-import { listen, type UnlistenFn } from '@tauri-apps/api/event';
+import { type UnlistenFn } from '@tauri-apps/api/event';
+import { safeListenEvent } from '../lib/safe-tauri';
 import { Paperclip, SquarePen, ArrowUp, MessageSquare, Download, X, FileText, Image as ImageIcon } from 'lucide-react';
 import { Button, EmptyState, MessageListSkeleton, LoadingDots } from './ui';
 import { ResizableChatLayout } from './ai/ResizableChatLayout';
@@ -160,7 +161,7 @@ export function ChatArea() {
   // Listen for hand-execution-complete Tauri events
   useEffect(() => {
     let unlisten: UnlistenFn | undefined;
-    listen<{ approvalId: string; handId: string; success: boolean; error?: string | null }>(
+    safeListenEvent<{ approvalId: string; handId: string; success: boolean; error?: string | null }>(
       'hand-execution-complete',
       (event) => {
         const { handId, success, error } = event.payload;