Vendor backend and frontend into the monorepo

The submodule collapse was only half applied: .gitmodules was deleted but
backend/ and frontend/ were still recorded as gitlinks, so none of their
files were tracked. Replace the gitlinks with the real trees.

Also untrack .env (it carried placeholder secrets) in favour of a tracked
.env.example, drop the committed __pycache__, and narrow the blanket *.png
ignore that would have swallowed design assets.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/main.tsx

@@ -0,0 +1,52 @@
+import {
+  MutationCache,
+  QueryCache,
+  QueryClient,
+  QueryClientProvider,
+} from "@tanstack/react-query"
+import { createRouter, RouterProvider } from "@tanstack/react-router"
+import { StrictMode } from "react"
+import ReactDOM from "react-dom/client"
+import { ApiError, OpenAPI } from "./client"
+import { ThemeProvider } from "./components/theme-provider"
+import { Toaster } from "./components/ui/sonner"
+import "./index.css"
+import { routeTree } from "./routeTree.gen"
+
+OpenAPI.BASE = import.meta.env.VITE_API_URL
+OpenAPI.TOKEN = async () => {
+  return localStorage.getItem("access_token") || ""
+}
+
+const handleApiError = (error: Error) => {
+  if (error instanceof ApiError && [401, 403].includes(error.status)) {
+    localStorage.removeItem("access_token")
+    window.location.href = "/login"
+  }
+}
+const queryClient = new QueryClient({
+  queryCache: new QueryCache({
+    onError: handleApiError,
+  }),
+  mutationCache: new MutationCache({
+    onError: handleApiError,
+  }),
+})
+
+const router = createRouter({ routeTree })
+declare module "@tanstack/react-router" {
+  interface Register {
+    router: typeof router
+  }
+}
+
+ReactDOM.createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
+      <QueryClientProvider client={queryClient}>
+        <RouterProvider router={router} />
+        <Toaster richColors closeButton />
+      </QueryClientProvider>
+    </ThemeProvider>
+  </StrictMode>,
+)