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>

backend/tests/api/routes/test_private.py

@@ -0,0 +1,26 @@
+from fastapi.testclient import TestClient
+from sqlmodel import Session, select
+
+from app.core.config import settings
+from app.models import User
+
+
+def test_create_user(client: TestClient, db: Session) -> None:
+    r = client.post(
+        f"{settings.API_V1_STR}/private/users/",
+        json={
+            "email": "pollo@listo.com",
+            "password": "password123",
+            "full_name": "Pollo Listo",
+        },
+    )
+
+    assert r.status_code == 200
+
+    data = r.json()
+
+    user = db.exec(select(User).where(User.id == data["id"])).first()
+
+    assert user
+    assert user.email == "pollo@listo.com"
+    assert user.full_name == "Pollo Listo"