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/utils/utils.py

@@ -0,0 +1,26 @@
+import random
+import string
+
+from fastapi.testclient import TestClient
+
+from app.core.config import settings
+
+
+def random_lower_string() -> str:
+    return "".join(random.choices(string.ascii_lowercase, k=32))
+
+
+def random_email() -> str:
+    return f"{random_lower_string()}@{random_lower_string()}.com"
+
+
+def get_superuser_token_headers(client: TestClient) -> dict[str, str]:
+    login_data = {
+        "username": settings.FIRST_SUPERUSER,
+        "password": settings.FIRST_SUPERUSER_PASSWORD,
+    }
+    r = client.post(f"{settings.API_V1_STR}/login/access-token", data=login_data)
+    tokens = r.json()
+    a_token = tokens["access_token"]
+    headers = {"Authorization": f"Bearer {a_token}"}
+    return headers