refactor(test): share container fixtures across the integration and e2e suites

Why:
- tests/e2e/ cannot reach fixtures defined in a per-boundary conftest, and
  `pytest_plugins` is only honoured in the root conftest.

Changes:
- move the Postgres/MinIO/Qdrant container fixtures into
  tests/support/containers.py and register it as a root plugin
- fold MinIO bucket creation into `minio_settings`; an autouse fixture in a
  globally registered plugin would pull a container into unit runs
- add a `postgres_settings` fixture so a component can be built from it directly

Impact:
- no behavior change; `pytest -m unit` still needs no Docker

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/integration/qdrant/conftest.py

@@ -1,52 +0,0 @@
-import uuid
-from collections.abc import AsyncIterator, Iterator
-
-import pytest
-import pytest_asyncio
-from qdrant_client import AsyncQdrantClient
-from testcontainers.community.qdrant import QdrantContainer
-
-from src.config import QdrantSettings
-from src.infrastructure.qdrant.client import create_client
-
-# Pinned to match the `qdrant-client` major/minor in pyproject.toml. The
-# testcontainers default image trails it far enough that the client emits an
-# incompatibility warning, and testing against a version we do not deploy is
-# the wrong signal anyway.
-_QDRANT_IMAGE = "qdrant/qdrant:v1.19.0"
-
-
-@pytest.fixture(scope="session")
-def qdrant_container() -> Iterator[QdrantContainer]:
-    with QdrantContainer(image=_QDRANT_IMAGE) as container:
-        yield container
-
-
-@pytest.fixture(scope="session")
-def qdrant_url(qdrant_container: QdrantContainer) -> str:
-    """The container's REST URL, pinned to IPv4.
-
-    Same gotcha as postgres_url/minio_settings (see their conftests):
-    testcontainers reports the host as `localhost`, which resolves to `::1`
-    first, but Docker publishes the mapped port on IPv4 only. The IPv6 SYN is
-    dropped rather than refused, so the client hangs until its timeout instead
-    of falling back to the second address -- the connection does not fail, it
-    hangs.
-    """
-    host = qdrant_container.get_container_host_ip().replace("localhost", "127.0.0.1")
-    return f"http://{host}:{qdrant_container.get_exposed_port(6333)}"
-
-
-@pytest.fixture
-def qdrant_settings(qdrant_url: str) -> QdrantSettings:
-    """Settings naming a collection unique to this test (ADR-0016 isolation)."""
-    return QdrantSettings(url=qdrant_url, collection=f"chunks_{uuid.uuid4().hex}")
-
-
-@pytest_asyncio.fixture(loop_scope="session")
-async def qdrant_client(qdrant_settings: QdrantSettings) -> AsyncIterator[AsyncQdrantClient]:
-    client = create_client(qdrant_settings)
-    try:
-        yield client
-    finally:
-        await client.close()