Admin: allow changing your own quota

The self-protection guard refused every change to the admin's own account.
It now only refuses blocking and deleting yourself; a quota change is fine.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/tests/api/test_admin_users.py

@@ -168,6 +168,20 @@ async def test_admin_cannot_block_or_delete_themselves(world: World) -> None:
         assert (await c.delete(f"/api/admin/users/{admin.id}")).status_code == 409
 
 
+async def test_admin_can_change_their_own_quota(world: World) -> None:
+    admin = await world.user(admin=True)
+    async with await world.client(admin) as c:
+        resp = await c.patch(f"/api/admin/users/{admin.id}", json={"quota_bytes": 5 * 2**30})
+        assert resp.status_code == 200
+        assert resp.json()["quota_bytes"] == 5 * 2**30
+        # Quota together with a block is still refused: the block is the problem.
+        assert (
+            await c.patch(
+                f"/api/admin/users/{admin.id}", json={"quota_bytes": 2**30, "blocked": True}
+            )
+        ).status_code == 409
+
+
 async def test_delete_removes_the_user_and_their_data(world: World, bus: _Bus) -> None:
     admin = await world.user(admin=True)
     target = await world.user()