Subscriber resilience and RabbitMQ fixes (#765)

Subscriber resilience: recreate consumer after connection failure

- Move consumer creation from Subscriber.start() into the run() loop,
  matching the pattern used by Consumer. If the connection drops and the
  consumer is closed in the finally block, the loop now recreates it on
  the next iteration instead of spinning forever on a None consumer.

Consumer thread safety:
- Dedicated ThreadPoolExecutor per consumer so all pika operations
  (create, receive, acknowledge, negative_acknowledge) run on the
  same thread — pika BlockingConnection is not thread-safe
- Applies to both Consumer and Subscriber classes

Config handler type audit — fix four mismatched type registrations:
- librarian: was ["librarian"] (non-existent type), now ["flow",
  "active-flow"] (matches config["flow"] that the handler reads)
- cores/service: was ["kg-core"], now ["flow"] (reads
  config["flow"])
- metering/counter: was ["token-costs"], now ["token-cost"]
  (singular)
- agent/mcp_tool: was ["mcp-tool"], now ["mcp"] (reads
  config["mcp"])

Update tests

tests/unit/test_concurrency/test_consumer_concurrency.py

@@ -81,9 +81,8 @@ class TestTaskGroupConcurrency:
 
         # Track how many consume_from_queue calls are made
         call_count = 0
-        original_running = True
 
-        async def mock_consume(backend_consumer):
+        async def mock_consume(backend_consumer, executor=None):
             nonlocal call_count
             call_count += 1
             # Wait a bit to let all tasks start, then signal stop
@@ -107,7 +106,7 @@ class TestTaskGroupConcurrency:
         consumer = _make_consumer(concurrency=1)
         call_count = 0
 
-        async def mock_consume(backend_consumer):
+        async def mock_consume(backend_consumer, executor=None):
             nonlocal call_count
             call_count += 1
             await asyncio.sleep(0.01)
@@ -294,9 +293,8 @@ class TestPollTimeout:
             raise type('Timeout', (Exception,), {})("timeout")
 
         mock_pulsar_consumer.receive = capture_receive
-        consumer.consumer = mock_pulsar_consumer
 
-        await consumer.consume_from_queue()
+        await consumer.consume_from_queue(mock_pulsar_consumer)
 
         assert received_kwargs.get("timeout_millis") == 100