feat: workspace-based multi-tenancy, replacing user as tenancy axis (#840)

Introduces `workspace` as the isolation boundary for config, flows,
library, and knowledge data. Removes `user` as a schema-level field
throughout the code, API specs, and tests; workspace provides the
same separation more cleanly at the trusted flow.workspace layer
rather than through client-supplied message fields.

Design
------
- IAM tech spec (docs/tech-specs/iam.md) documents current state,
  proposed auth/access model, and migration direction.
- Data ownership model (docs/tech-specs/data-ownership-model.md)
  captures the workspace/collection/flow hierarchy.

Schema + messaging
------------------
- Drop `user` field from AgentRequest/Step, GraphRagQuery,
  DocumentRagQuery, Triples/Graph/Document/Row EmbeddingsRequest,
  Sparql/Rows/Structured QueryRequest, ToolServiceRequest.
- Keep collection/workspace routing via flow.workspace at the
  service layer.
- Translators updated to not serialise/deserialise user.

API specs
---------
- OpenAPI schemas and path examples cleaned of user fields.
- Websocket async-api messages updated.
- Removed the unused parameters/User.yaml.

Services + base
---------------
- Librarian, collection manager, knowledge, config: all operations
  scoped by workspace. Config client API takes workspace as first
  positional arg.
- `flow.workspace` set at flow start time by the infrastructure;
  no longer pass-through from clients.
- Tool service drops user-personalisation passthrough.

CLI + SDK
---------
- tg-init-workspace and workspace-aware import/export.
- All tg-* commands drop user args; accept --workspace.
- Python API/SDK (flow, socket_client, async_*, explainability,
  library) drop user kwargs from every method signature.

MCP server
----------
- All tool endpoints drop user parameters; socket_manager no longer
  keyed per user.

Flow service
------------
- Closure-based topic cleanup on flow stop: only delete topics
  whose blueprint template was parameterised AND no remaining
  live flow (across all workspaces) still resolves to that topic.
  Three scopes fall out naturally from template analysis:
    * {id} -> per-flow, deleted on stop
    * {blueprint} -> per-blueprint, kept while any flow of the
      same blueprint exists
    * {workspace} -> per-workspace, kept while any flow in the
      workspace exists
    * literal -> global, never deleted (e.g. tg.request.librarian)
  Fixes a bug where stopping a flow silently destroyed the global
  librarian exchange, wedging all library operations until manual
  restart.

RabbitMQ backend
----------------
- heartbeat=60, blocked_connection_timeout=300. Catches silently
  dead connections (broker restart, orphaned channels, network
  partitions) within ~2 heartbeat windows, so the consumer
  reconnects and re-binds its queue rather than sitting forever
  on a zombie connection.

Tests
-----
- Full test refresh: unit, integration, contract, provenance.
- Dropped user-field assertions and constructor kwargs across
  ~100 test files.
- Renamed user-collection isolation tests to workspace-collection.

tests/integration/test_rows_graphql_query_integration.py

@@ -154,7 +154,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_schema_configuration_and_generation(self, processor, sample_schema_config):
         """Test schema configuration loading and GraphQL schema generation"""
         # Load schema configuration
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         
         # Verify schemas were loaded
         assert len(processor.schemas) == 2
@@ -181,7 +181,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_cassandra_connection_and_table_creation(self, processor, sample_schema_config):
         """Test Cassandra connection and dynamic table creation"""
         # Load schema configuration
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         
         # Connect to Cassandra
         processor.connect_cassandra()
@@ -218,7 +218,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_data_insertion_and_graphql_query(self, processor, sample_schema_config):
         """Test inserting data and querying via GraphQL"""
         # Load schema and connect
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         processor.connect_cassandra()
         
         # Setup test data
@@ -292,7 +292,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_graphql_query_with_filters(self, processor, sample_schema_config):
         """Test GraphQL queries with filtering on indexed fields"""
         # Setup (reuse previous setup)
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         processor.connect_cassandra()
         
         keyspace = "test_user"
@@ -353,7 +353,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_graphql_error_handling(self, processor, sample_schema_config):
         """Test GraphQL error handling for invalid queries"""
         # Setup
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         
         # Test invalid field query
         invalid_query = '''
@@ -386,7 +386,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_message_processing_integration(self, processor, sample_schema_config):
         """Test full message processing workflow"""
         # Setup
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         processor.connect_cassandra()
         
         # Create mock message
@@ -432,7 +432,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_concurrent_queries(self, processor, sample_schema_config):
         """Test handling multiple concurrent GraphQL queries"""
         # Setup
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         processor.connect_cassandra()
         
         # Create multiple query tasks
@@ -476,7 +476,7 @@ class TestObjectsGraphQLQueryIntegration:
             }
         }
         
-        await processor.on_schema_config(initial_config, version=1)
+        await processor.on_schema_config("default", initial_config, version=1)
         assert len(processor.schemas) == 1
         assert "simple" in processor.schemas
         
@@ -500,7 +500,7 @@ class TestObjectsGraphQLQueryIntegration:
             }
         }
         
-        await processor.on_schema_config(updated_config, version=2)
+        await processor.on_schema_config("default", updated_config, version=2)
         
         # Verify updated schemas
         assert len(processor.schemas) == 2
@@ -518,7 +518,7 @@ class TestObjectsGraphQLQueryIntegration:
     async def test_large_result_set_handling(self, processor, sample_schema_config):
         """Test handling of large query result sets"""
         # Setup
-        await processor.on_schema_config(sample_schema_config, version=1)
+        await processor.on_schema_config("default", sample_schema_config, version=1)
         processor.connect_cassandra()
         
         keyspace = "large_test_user"
@@ -601,7 +601,7 @@ class TestObjectsGraphQLQueryPerformance:
             }
         }
         
-        await processor.on_schema_config(schema_config, version=1)
+        await processor.on_schema_config("default", schema_config, version=1)
         
         # Measure query execution time
         start_time = time.time()