feat: US-003 — electron-trpc IPC bridge and appRouter scaffold

- Install electron-trpc, @trpc/server, @trpc/client, @trpc/react-query, @tanstack/react-query, zod
- Create appRouter in src/main/router/index.ts with stub routers for: health, clients, projects, tasks, checkpoints, notes, ai
- health.ping procedure returns 'pong'
- All procedure inputs validated with Zod schemas
- Configure IPC handler in main process (createIPCHandler) and preload (exposeElectronTRPC)
- Create renderer trpc client in src/renderer/lib/trpc.ts with ipcLink
- Wrap app with TRPCProvider + QueryClientProvider in src/renderer/index.tsx
- Verify health.ping in HomePage component (shows 'tRPC IPC bridge: pong')
- Typecheck passes

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

src/renderer/index.tsx

@@ -1,14 +1,34 @@
-import { StrictMode } from 'react';
+import { StrictMode, useState } from 'react';
 import { createRoot } from 'react-dom/client';
 import { RouterProvider } from '@tanstack/react-router';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
+import { ipcLink } from 'electron-trpc/renderer';
 import { router } from './router';
+import { trpc } from './lib/trpc';
 import './globals.css';
 
+function App() {
+  const [queryClient] = useState(() => new QueryClient());
+  const [trpcClient] = useState(() =>
+    trpc.createClient({
+      links: [ipcLink()],
+    }),
+  );
+
+  return (
+    <trpc.Provider client={trpcClient} queryClient={queryClient}>
+      <QueryClientProvider client={queryClient}>
+        <RouterProvider router={router} />
+      </QueryClientProvider>
+    </trpc.Provider>
+  );
+}
+
 const rootElement = document.getElementById('root');
 if (!rootElement) throw new Error('Root element not found');
 
 createRoot(rootElement).render(
   <StrictMode>
-    <RouterProvider router={router} />
+    <App />
   </StrictMode>,
 );