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_reliability/test_metadata_preservation.py

@@ -35,7 +35,7 @@ class TestDocumentMetadataTranslator:
             "parent-id": "doc-100",
             "document-type": "page",
         }
-        obj = self.tx.to_pulsar(data)
+        obj = self.tx.decode(data)
         assert obj.id == "doc-123"
         assert obj.time == 1710000000
         assert obj.kind == "application/pdf"
@@ -45,14 +45,14 @@ class TestDocumentMetadataTranslator:
         assert obj.parent_id == "doc-100"
         assert obj.document_type == "page"
 
-        wire = self.tx.from_pulsar(obj)
+        wire = self.tx.encode(obj)
         assert wire["id"] == "doc-123"
         assert wire["user"] == "alice"
         assert wire["parent-id"] == "doc-100"
         assert wire["document-type"] == "page"
 
     def test_defaults_for_missing_fields(self):
-        obj = self.tx.to_pulsar({})
+        obj = self.tx.decode({})
         assert obj.parent_id == ""
         assert obj.document_type == "source"
 
@@ -63,25 +63,25 @@ class TestDocumentMetadataTranslator:
             "o": {"t": "i", "i": "http://example.org/o"},
         }]
         data = {"metadata": triple_wire}
-        obj = self.tx.to_pulsar(data)
+        obj = self.tx.decode(data)
         assert len(obj.metadata) == 1
         assert obj.metadata[0].s.iri == "http://example.org/s"
 
     def test_none_metadata_handled(self):
         data = {"metadata": None}
-        obj = self.tx.to_pulsar(data)
+        obj = self.tx.decode(data)
         assert obj.metadata == []
 
     def test_empty_tags_preserved(self):
         data = {"tags": []}
-        obj = self.tx.to_pulsar(data)
-        wire = self.tx.from_pulsar(obj)
+        obj = self.tx.decode(data)
+        wire = self.tx.encode(obj)
         assert wire["tags"] == []
 
     def test_falsy_fields_omitted_from_wire(self):
         """Empty string fields should be omitted from wire format."""
         obj = DocumentMetadata(id="", time=0, user="")
-        wire = self.tx.from_pulsar(obj)
+        wire = self.tx.encode(obj)
         assert "id" not in wire
         assert "user" not in wire
 
@@ -105,7 +105,7 @@ class TestProcessingMetadataTranslator:
             "collection": "my-collection",
             "tags": ["tag1"],
         }
-        obj = self.tx.to_pulsar(data)
+        obj = self.tx.decode(data)
         assert obj.id == "proc-1"
         assert obj.document_id == "doc-123"
         assert obj.flow == "default"
@@ -113,32 +113,32 @@ class TestProcessingMetadataTranslator:
         assert obj.collection == "my-collection"
         assert obj.tags == ["tag1"]
 
-        wire = self.tx.from_pulsar(obj)
+        wire = self.tx.encode(obj)
         assert wire["id"] == "proc-1"
         assert wire["document-id"] == "doc-123"
         assert wire["user"] == "alice"
         assert wire["collection"] == "my-collection"
 
     def test_missing_fields_use_defaults(self):
-        obj = self.tx.to_pulsar({})
+        obj = self.tx.decode({})
         assert obj.id is None
         assert obj.user is None
         assert obj.collection is None
 
     def test_tags_none_omitted(self):
         obj = ProcessingMetadata(tags=None)
-        wire = self.tx.from_pulsar(obj)
+        wire = self.tx.encode(obj)
         assert "tags" not in wire
 
     def test_tags_empty_list_preserved(self):
         obj = ProcessingMetadata(tags=[])
-        wire = self.tx.from_pulsar(obj)
+        wire = self.tx.encode(obj)
         assert wire["tags"] == []
 
     def test_user_and_collection_preserved(self):
         """Core pipeline routing fields must survive round-trip."""
         data = {"user": "bob", "collection": "research"}
-        obj = self.tx.to_pulsar(data)
-        wire = self.tx.from_pulsar(obj)
+        obj = self.tx.decode(data)
+        wire = self.tx.encode(obj)
         assert wire["user"] == "bob"
         assert wire["collection"] == "research"