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/postgres/conftest.py

@@ -1,98 +0,0 @@
-from collections.abc import AsyncIterator, Iterator
-
-import pytest
-import pytest_asyncio
-from alembic.command import upgrade
-from alembic.config import Config
-from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession, async_sessionmaker
-from testcontainers.community.postgres import PostgresContainer
-
-from src.config import PostgresSettings
-from src.infrastructure.postgres.database import create_engine
-
-
-def _alembic_config(database_url: str) -> Config:
-    config = Config("alembic.ini")
-    config.set_main_option("sqlalchemy.url", database_url)
-    return config
-
-
-def _settings_from_url(url: str) -> PostgresSettings:
-    # testcontainers returns postgresql+asyncpg://user:pass@host:port/db ;
-    # PostgresSettings builds its own dsn from parts, so parse the parts back out.
-    without_scheme = url.split("://", 1)[1]
-    creds, hostpart = without_scheme.split("@", 1)
-    user, password = creds.split(":", 1)
-    hostport, db = hostpart.split("/", 1)
-    host, port = hostport.split(":", 1)
-    return PostgresSettings(host=host, port=int(port), user=user, password=password, db=db)
-
-
-@pytest.fixture(scope="session")
-def postgres_container() -> Iterator[PostgresContainer]:
-    with PostgresContainer("postgres:17", driver="asyncpg") as container:
-        yield container
-
-
-@pytest.fixture(scope="session")
-def postgres_url(postgres_container: PostgresContainer) -> str:
-    """The container's URL, pinned to IPv4.
-
-    Testcontainers reports the host as `localhost`, which resolves to `::1`
-    before `127.0.0.1`. Docker publishes the mapped port on IPv4 only, and the
-    IPv6 SYN is dropped rather than refused, so asyncpg blocks on the first
-    address until its connect timeout instead of falling back to the second --
-    the connection does not fail, it hangs.
-    """
-    return postgres_container.get_connection_url().replace("@localhost:", "@127.0.0.1:")
-
-
-@pytest.fixture(scope="session")
-def migrated_postgres_url(postgres_url: str) -> str:
-    """The container's URL, after Alembic has created the schema on it once."""
-    upgrade(_alembic_config(postgres_url), "head")
-    return postgres_url
-
-
-@pytest_asyncio.fixture(scope="session", loop_scope="session")
-async def postgres_engine(migrated_postgres_url: str) -> AsyncIterator[AsyncEngine]:
-    engine = create_engine(_settings_from_url(migrated_postgres_url))
-    try:
-        yield engine
-    finally:
-        await engine.dispose()
-
-
-@pytest_asyncio.fixture(loop_scope="session")
-async def db_sessionmaker(
-    postgres_engine: AsyncEngine,
-) -> AsyncIterator[async_sessionmaker[AsyncSession]]:
-    """A session *factory* per test, bound to a rolled-back outer transaction.
-
-    Every session it produces shares one connection/outer transaction, so
-    writes `commit()`ed by one session are visible to the next -- needed for
-    code under test that opens more than one session per operation (auth
-    resolution, the ADR-0017 two-phase upload) -- while the whole test's
-    writes still roll back together at teardown (ADR-0016: isolate data per
-    test).
-    """
-    async with postgres_engine.connect() as connection:
-        outer_transaction = await connection.begin()
-        sessionmaker = async_sessionmaker(
-            bind=connection, expire_on_commit=False, join_transaction_mode="create_savepoint"
-        )
-        yield sessionmaker
-        await outer_transaction.rollback()
-
-
-@pytest_asyncio.fixture(loop_scope="session")
-async def db_session(
-    db_sessionmaker: async_sessionmaker[AsyncSession],
-) -> AsyncIterator[AsyncSession]:
-    """One session per test, bound to a rolled-back outer transaction.
-
-    Isolates each test's writes (ADR-0016: isolate data per test) without
-    needing a fresh container or unique keys per test.
-    """
-    async with db_sessionmaker() as session:
-        yield session