RabbitMQ fixes: thread safety, subscriber resilience, config errors

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

Subscriber resilience:
- Move consumer creation from start() into the run() loop so it is
  recreated after connection failures instead of spinning on None

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)