refactor: address PR #851 review round 3 (ingest transport)

- LocalTransport.run_consumers increments active_consumer_count per worker
  (instead of once after the loop) so the count is accurate if a later
  tg.start() raises mid-pool.
- Add LocalTransport.aclose() to explicitly close its owned send/receive stream
  ends (belt-and-suspenders against unclosed-resource warnings; anyio aclose is
  idempotent, and by shutdown the scanner is already winding down). Reworded the
  base IngestTransport.aclose() docstring to point at the overrides.
- Inline ingest_transport.producer at the scanner/user_manager call sites,
  dropping the single-use task_producer alias in both lifespan paths.
- Annotate DistributedTransport._producer explicitly as ProcrastinateTaskProducer
  so the drain() coupling is visible and ty catches drift.
- Add a unit test for LocalTransport.aclose() (closes the owned streams,
  idempotent).

Refs: Deck #196

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/vector/test_ingest_transport.py

@@ -23,6 +23,7 @@ from nextcloud_mcp_server.vector.queue import (
     SpawnWorker,
     build_transport,
 )
+from nextcloud_mcp_server.vector.scanner import DocumentTask
 
 pytestmark = pytest.mark.unit
 
@@ -94,6 +95,25 @@ class TestLocalTransport:
         assert all(s is not None for s in received_streams)
         assert len({id(s) for s in received_streams}) == 3
 
+    async def test_aclose_closes_owned_streams_idempotently(self):
+        transport = LocalTransport(max_buffer_size=5)
+        await transport.aclose()
+
+        # The send end is closed → the producer raises rather than silently
+        # dropping (the producer wraps the same stream aclose() closed).
+        with pytest.raises(anyio.ClosedResourceError):
+            await transport.producer.send(
+                DocumentTask(
+                    user_id="u",
+                    doc_id="1",
+                    doc_type="note",
+                    operation="index",
+                    modified_at=0,
+                )
+            )
+        # Idempotent: closing again is a no-op, not an error.
+        await transport.aclose()
+
 
 class TestDistributedTransport:
     async def test_run_consumers_is_noop(self):