feat: TDD Phase 1 — 44 backend API tests passing

Test infrastructure:
- conftest.py with SQLite in-memory DB, isolated per-test cleanup
- pytest.ini with asyncio auto mode
- Fixtures: admin/dba/developer/guest/disabled users, tokens, test instance

Test coverage (44 tests):
- test_auth: login/logout/me/token expiry (8 tests)
- test_users: CRUD + role permissions (8 tests)
- test_instances: CRUD + connection test mock (8 tests)
- test_tickets: CRUD + review/execute workflow + pagination (11 tests)
- test_query: select/drop/delete rejection + guest deny (4 tests)
- test_dashboard: stats + auth check (2 tests)

Backend fix:
- query endpoint now catches ValueError from QueryService → 400 instead of 500

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/tests/test_query.py

@@ -0,0 +1,70 @@
+import sys
+from unittest.mock import patch, AsyncMock, MagicMock
+
+from httpx import AsyncClient
+
+from tests.conftest import auth_header
+
+
+def _make_aiomysql_mock():
+    aiomysql = MagicMock()
+    aiomysql.connect = AsyncMock()
+    aiomysql.DictCursor = MagicMock()
+    return aiomysql
+
+
+class TestExecuteQuery:
+    async def test_select_query(self, client: AsyncClient, test_instance, admin_token):
+        from contextlib import asynccontextmanager
+
+        mock_cursor = AsyncMock()
+        mock_cursor.description = [("id",), ("name",)]
+        mock_cursor.fetchall.return_value = [{"id": 1, "name": "test"}]
+        mock_cursor.execute = AsyncMock()
+
+        @asynccontextmanager
+        async def mock_cursor_ctx(*args, **kwargs):
+            yield mock_cursor
+
+        mock_conn = AsyncMock()
+        mock_conn.cursor = mock_cursor_ctx
+        mock_conn.close = MagicMock()
+
+        mock_aiomysql = _make_aiomysql_mock()
+        mock_aiomysql.connect = AsyncMock(return_value=mock_conn)
+        mock_aiomysql.DictCursor = MagicMock()
+
+        with patch.dict(sys.modules, {"aiomysql": mock_aiomysql}):
+            resp = await client.post("/api/v1/query", headers=auth_header(admin_token), json={
+                "instance_id": test_instance.id,
+                "database": "test_db",
+                "sql": "SELECT * FROM users LIMIT 10",
+            })
+            assert resp.status_code == 200
+            data = resp.json()
+            assert "columns" in data
+            assert "rows" in data
+
+    async def test_drop_rejected(self, client: AsyncClient, test_instance, admin_token):
+        resp = await client.post("/api/v1/query", headers=auth_header(admin_token), json={
+            "instance_id": test_instance.id,
+            "database": "test_db",
+            "sql": "DROP TABLE users",
+        })
+        assert resp.status_code == 400
+
+    async def test_delete_rejected(self, client: AsyncClient, test_instance, admin_token):
+        resp = await client.post("/api/v1/query", headers=auth_header(admin_token), json={
+            "instance_id": test_instance.id,
+            "database": "test_db",
+            "sql": "DELETE FROM users WHERE 1=1",
+        })
+        assert resp.status_code == 400
+
+    async def test_guest_cannot_query(self, client: AsyncClient, test_instance, guest_token):
+        resp = await client.post("/api/v1/query", headers=auth_header(guest_token), json={
+            "instance_id": test_instance.id,
+            "database": "test_db",
+            "sql": "SELECT 1",
+        })
+        assert resp.status_code == 403