Pub/sub abstraction: decouple from Pulsar (#751)

Remove Pulsar-specific concepts from application code so that
the pub/sub backend is swappable via configuration.

Rename translators:
- to_pulsar/from_pulsar → decode/encode across all translator
  classes, dispatch handlers, and tests (55+ files)
- from_response_with_completion → encode_with_completion
- Remove pulsar.schema.Record from translator base class

Queue naming (CLASS:TOPICSPACE:TOPIC):
- Replace topic() helper with queue() using new format:
  flow:tg:name, request:tg:name, response:tg:name, state:tg:name
- Queue class implies persistence/TTL (no QoS in names)
- Update Pulsar backend map_topic() to parse new format
- Librarian queues use flow class (persistent, for chunking)
- Config push uses state class (persistent, last-value)
- Remove 15 dead topic imports from schema files
- Update init_trustgraph.py namespace: config → state

Confine Pulsar to pulsar_backend.py:
- Delete legacy PulsarClient class from pubsub.py
- Move add_args to add_pubsub_args() with standalone flag
  for CLI tools (defaults to localhost)
- PulsarBackendConsumer.receive() catches _pulsar.Timeout,
  raises standard TimeoutError
- Remove Pulsar imports from: async_processor, flow_processor,
  log_level, all 11 client files, 4 storage writers, gateway
  service, gateway config receiver
- Remove log_level/LoggerLevel from client API
- Rewrite tg-monitor-prompts to use backend abstraction
- Update tg-dump-queues to use add_pubsub_args

Also: pubsub-abstraction.md tech spec covering problem statement,
design goals, as-is requirements, candidate broker assessment,
approach, and implementation order.

tests/unit/test_gateway/test_dispatch_config.py

@@ -49,7 +49,7 @@ class TestConfigRequestor:
         mock_translator_registry.get_response_translator.return_value = Mock()
         
         # Setup translator response
-        mock_request_translator.to_pulsar.return_value = "translated_request"
+        mock_request_translator.decode.return_value = "translated_request"
         
         # Patch ServiceRequestor async methods with regular mocks (not AsyncMock)
         with patch.object(ServiceRequestor, 'start', return_value=None), \
@@ -64,7 +64,7 @@ class TestConfigRequestor:
         result = requestor.to_request({"test": "body"})
         
         # Verify translator was called correctly
-        mock_request_translator.to_pulsar.assert_called_once_with({"test": "body"})
+        mock_request_translator.decode.assert_called_once_with({"test": "body"})
         assert result == "translated_request"
 
     @patch('trustgraph.gateway.dispatch.config.TranslatorRegistry')
@@ -76,7 +76,7 @@ class TestConfigRequestor:
         mock_translator_registry.get_response_translator.return_value = mock_response_translator
         
         # Setup translator response
-        mock_response_translator.from_response_with_completion.return_value = "translated_response"
+        mock_response_translator.encode_with_completion.return_value = "translated_response"
         
         requestor = ConfigRequestor(
             backend=Mock(),
@@ -89,5 +89,5 @@ class TestConfigRequestor:
         result = requestor.from_response(mock_message)
         
         # Verify translator was called correctly
-        mock_response_translator.from_response_with_completion.assert_called_once_with(mock_message)
+        mock_response_translator.encode_with_completion.assert_called_once_with(mock_message)
         assert result == "translated_response"