Add missing test for DELETE /profile/{username} endpoint

[anxkhn]

Context

The DELETE /profile/{username} endpoint exists in app/main.py but has no corresponding test in tests/test_profile.py. Every endpoint should have at least basic test coverage.

Steps to reproduce

1. Run: pytest tests/test_profile.py -v
2. Observe there is no test for the delete endpoint.
3. Check tests/test_profile.py -- only test_create_profile, test_get_profile, and test_get_nonexistent_profile exist.

Expected behavior

There should be at least one test that verifies:

• Deleting an existing profile returns 200 and {"deleted": true}
• Deleting a non-existent profile returns 404

Actual behavior

No test exists for the DELETE /profile/{username} endpoint.

Files

• tests/test_profile.py -- add new test function(s) here

Acceptance criteria

• A test exists that creates a profile, deletes it, and verifies the response
• A test exists that attempts to delete a non-existent profile and verifies 404
• All tests pass: pytest tests/test_profile.py -v

Suggested approach

1. Open tests/test_profile.py.
2. Add a test function like:

   def test_delete_profile(clean_store):
       client.post("/profile", json={"username": "charlie", "bio": "tester"})
       response = client.delete("/profile/charlie")
       assert response.status_code == 200
       assert response.json() == {"deleted": True}
       # Verify it is actually gone
       get_response = client.get("/profile/charlie")
       assert get_response.status_code == 404

3. Optionally add a test for deleting a non-existent profile.
4. Run pytest tests/test_profile.py -v.