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_retrieval/test_structured_diag/test_message_translation.py

@@ -28,7 +28,7 @@ class TestRequestTranslation:
         }
 
         # Translate to Pulsar
-        pulsar_msg = translator.to_pulsar(api_data)
+        pulsar_msg = translator.decode(api_data)
 
         assert pulsar_msg.operation == "schema-selection"
         assert pulsar_msg.sample == "test data sample"
@@ -46,7 +46,7 @@ class TestRequestTranslation:
             "options": {"delimiter": ","}
         }
 
-        pulsar_msg = translator.to_pulsar(api_data)
+        pulsar_msg = translator.decode(api_data)
 
         assert pulsar_msg.operation == "generate-descriptor"
         assert pulsar_msg.sample == "csv data"
@@ -70,7 +70,7 @@ class TestResponseTranslation:
         )
 
         # Translate to API format
-        api_data = translator.from_pulsar(pulsar_response)
+        api_data = translator.encode(pulsar_response)
 
         assert api_data["operation"] == "schema-selection"
         assert api_data["schema-matches"] == ["products", "inventory", "catalog"]
@@ -86,7 +86,7 @@ class TestResponseTranslation:
             error=None
         )
 
-        api_data = translator.from_pulsar(pulsar_response)
+        api_data = translator.encode(pulsar_response)
 
         assert api_data["operation"] == "schema-selection"
         assert api_data["schema-matches"] == []
@@ -103,7 +103,7 @@ class TestResponseTranslation:
             error=None
         )
 
-        api_data = translator.from_pulsar(pulsar_response)
+        api_data = translator.encode(pulsar_response)
 
         assert api_data["operation"] == "detect-type"
         assert api_data["detected-type"] == "xml"
@@ -123,7 +123,7 @@ class TestResponseTranslation:
             )
         )
 
-        api_data = translator.from_pulsar(pulsar_response)
+        api_data = translator.encode(pulsar_response)
 
         assert api_data["operation"] == "schema-selection"
         # Error objects are typically handled separately by the gateway
@@ -146,7 +146,7 @@ class TestResponseTranslation:
             error=None
         )
 
-        api_data = translator.from_pulsar(pulsar_response)
+        api_data = translator.encode(pulsar_response)
 
         assert api_data["operation"] == "diagnose"
         assert api_data["detected-type"] == "csv"
@@ -165,7 +165,7 @@ class TestResponseTranslation:
             error=None
         )
 
-        api_data, is_final = translator.from_response_with_completion(pulsar_response)
+        api_data, is_final = translator.encode_with_completion(pulsar_response)
 
         assert is_final is True  # Structured-diag responses are always final
         assert api_data["operation"] == "schema-selection"