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/test_search.py

@@ -16,7 +16,9 @@ def _minimal_gif() -> bytes:
 
 
 @pytest.mark.asyncio
-async def test_and_filter_returns_only_matching_images(client):
+async def test_and_filter_returns_only_matching_images(authed_client):
+    client, token = authed_client
+    headers = {"Authorization": f"Bearer {token}"}
     data = _minimal_gif()
 
     # Image with both tags
@@ -24,6 +26,7 @@ async def test_and_filter_returns_only_matching_images(client):
         "/api/v1/images",
         files={"file": ("both.gif", io.BytesIO(data), "image/gif")},
         data={"tags": "andcat,andfunny"},
+        headers=headers,
     )
     both_id = r_both.json()["id"]
 
@@ -32,6 +35,7 @@ async def test_and_filter_returns_only_matching_images(client):
         "/api/v1/images",
         files={"file": ("one.gif", io.BytesIO(data + b"\x00"), "image/gif")},
         data={"tags": "andcat"},
+        headers=headers,
     )
 
     response = await client.get("/api/v1/images?tags=andcat,andfunny")
@@ -43,7 +47,9 @@ async def test_and_filter_returns_only_matching_images(client):
 
 
 @pytest.mark.asyncio
-async def test_filter_excludes_partial_tag_match(client):
+async def test_filter_excludes_partial_tag_match(authed_client):
+    client, token = authed_client
+    headers = {"Authorization": f"Bearer {token}"}
     data = _minimal_gif()
 
     # Image with only "exclcat"
@@ -51,6 +57,7 @@ async def test_filter_excludes_partial_tag_match(client):
         "/api/v1/images",
         files={"file": ("partial.gif", io.BytesIO(data + b"\x01"), "image/gif")},
         data={"tags": "exclcat"},
+        headers=headers,
     )
 
     # Filter requires both exclcat and exclother