Feat: Enforce PostgreSQL for integration tests; add Docker test stack

- conftest.py: pytest_configure guard rejects non-postgresql+asyncpg:// URLs
  before any test collects (per constitution §2.5/§5.2 v1.3.0)
- docker-compose.test.yml: isolated postgres-test (5433) + minio-test (9002)
  + api-test runner; one command runs the full suite against real PostgreSQL
- Makefile: test-unit and test-integration targets
- .env.test.example: documents variables needed to run tests outside Docker
- Fix pre-existing test bug: integration tests using client fixture (NoOpAuthProvider)
  for write operations (upload/delete/patch) now use authed_client with Bearer
  token — these were never caught because tests never ran against a live stack

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/tests/integration/conftest.py

@@ -1,5 +1,6 @@
 import os
 
+import pytest
 import pytest_asyncio
 from httpx import ASGITransport, AsyncClient
 from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
@@ -9,11 +10,11 @@ os.environ.setdefault("JWT_SECRET_KEY", "test-secret-key-for-testing-only")
 os.environ.setdefault("OWNER_USERNAME", "testowner")
 os.environ.setdefault("OWNER_PASSWORD", "testpassword")
 
-from app.auth.jwt_provider import JWTAuthProvider
-from app.config import get_settings
-from app.database import Base
-from app.dependencies import get_auth, get_db, get_storage
-from app.main import app
+from app.auth.jwt_provider import JWTAuthProvider  # noqa: E402
+from app.config import get_settings  # noqa: E402
+from app.database import Base  # noqa: E402
+from app.dependencies import get_auth, get_db, get_storage  # noqa: E402
+from app.main import app  # noqa: E402
 
 # Bust the LRU cache so get_settings() picks up the env vars set above
 get_settings.cache_clear()
@@ -26,8 +27,6 @@ _TEST_OWNER_PASSWORD = os.environ["OWNER_PASSWORD"]
 @pytest_asyncio.fixture(scope="session", loop_scope="session")
 async def engine():
     settings = get_settings()
-    # Use a separate test database URL if TEST_DATABASE_URL is set
-    import os
     db_url = os.getenv("TEST_DATABASE_URL", settings.database_url)
     eng = create_async_engine(db_url, echo=False)
     async with eng.begin() as conn:
@@ -108,3 +107,15 @@ async def authed_client(db_session, jwt_auth_provider):
         yield c, valid_token
 
     app.dependency_overrides.clear()
+
+
+def pytest_configure(config):
+    db_url = os.getenv("TEST_DATABASE_URL") or os.getenv("DATABASE_URL", "")
+    if not db_url.startswith("postgresql+asyncpg://"):
+        pytest.exit(
+            "Integration tests require a PostgreSQL database "
+            "(postgresql+asyncpg://...). "
+            "Set TEST_DATABASE_URL or DATABASE_URL accordingly. "
+            f"Got: {db_url!r}",
+            returncode=1,
+        )