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/routes/_layout/index.tsx

@@ -0,0 +1,31 @@
+import { createFileRoute } from "@tanstack/react-router"
+
+import useAuth from "@/hooks/useAuth"
+
+export const Route = createFileRoute("/_layout/")({
+  component: Dashboard,
+  head: () => ({
+    meta: [
+      {
+        title: "Dashboard - FastAPI Cloud",
+      },
+    ],
+  }),
+})
+
+function Dashboard() {
+  const { user: currentUser } = useAuth()
+
+  return (
+    <div>
+      <div>
+        <h1 className="text-2xl truncate max-w-sm">
+          Hi, {currentUser?.full_name || currentUser?.email} 👋
+        </h1>
+        <p className="text-muted-foreground">
+          Welcome back, nice to see you again!!!
+        </p>
+      </div>
+    </div>
+  )
+}