refactor: align backend layout and supabase infra

Consolidate backend modules/tests under the backend package while syncing Supabase compose/env config and related plans.

backend/tests/unit/core/test_base_service.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+import pytest
+from fastapi import HTTPException
+
+from uuid import UUID
+
+from core.auth.models import CurrentUser
+from core.db.base_service import BaseService
+
+
+def test_require_current_user_raises_when_missing() -> None:
+    service = BaseService(current_user=None)
+
+    with pytest.raises(HTTPException) as exc_info:
+        service.require_current_user()
+
+    assert exc_info.value.status_code == 401
+
+
+def test_require_current_user_returns_user() -> None:
+    user = CurrentUser(id=UUID("00000000-0000-0000-0000-000000000001"))
+    service = BaseService(current_user=user)
+
+    result = service.require_current_user()
+
+    assert result.id == user.id