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/unit/test_base/test_flow_processor.py

@@ -78,11 +78,11 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
         flow_name = 'test-flow'
         flow_defn = {'config': 'test-config'}
 
-        await processor.start_flow(flow_name, flow_defn)
+        await processor.start_flow("default", flow_name, flow_defn)
 
-        assert flow_name in processor.flows
+        assert ("default", flow_name) in processor.flows
         mock_flow_class.assert_called_once_with(
-            'test-processor', flow_name, processor, flow_defn
+            'test-processor', flow_name, "default", processor, flow_defn
         )
         mock_flow.start.assert_called_once()
 
@@ -103,11 +103,11 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
         mock_flow_class.return_value = mock_flow
 
         flow_name = 'test-flow'
-        await processor.start_flow(flow_name, {'config': 'test-config'})
+        await processor.start_flow("default", flow_name, {'config': 'test-config'})
 
-        await processor.stop_flow(flow_name)
+        await processor.stop_flow("default", flow_name)
 
-        assert flow_name not in processor.flows
+        assert ("default", flow_name) not in processor.flows
         mock_flow.stop.assert_called_once()
 
     @with_async_processor_patches
@@ -120,7 +120,7 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
 
         processor = FlowProcessor(**config)
 
-        await processor.stop_flow('non-existent-flow')
+        await processor.stop_flow("default", 'non-existent-flow')
 
         assert processor.flows == {}
 
@@ -146,11 +146,11 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
             }
         }
 
-        await processor.on_configure_flows(config_data, version=1)
+        await processor.on_configure_flows("default", config_data, version=1)
 
-        assert 'test-flow' in processor.flows
+        assert ("default", 'test-flow') in processor.flows
         mock_flow_class.assert_called_once_with(
-            'test-processor', 'test-flow', processor,
+            'test-processor', 'test-flow', "default", processor,
             {'config': 'test-config'}
         )
         mock_flow.start.assert_called_once()
@@ -171,7 +171,7 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
             }
         }
 
-        await processor.on_configure_flows(config_data, version=1)
+        await processor.on_configure_flows("default", config_data, version=1)
 
         assert processor.flows == {}
 
@@ -189,7 +189,7 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
             'other-data': 'some-value'
         }
 
-        await processor.on_configure_flows(config_data, version=1)
+        await processor.on_configure_flows("default", config_data, version=1)
 
         assert processor.flows == {}
 
@@ -216,7 +216,7 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
             }
         }
 
-        await processor.on_configure_flows(config_data1, version=1)
+        await processor.on_configure_flows("default", config_data1, version=1)
 
         config_data2 = {
             'processor:test-processor': {
@@ -224,12 +224,12 @@ class TestFlowProcessorSimple(IsolatedAsyncioTestCase):
             }
         }
 
-        await processor.on_configure_flows(config_data2, version=2)
+        await processor.on_configure_flows("default", config_data2, version=2)
 
-        assert 'flow1' not in processor.flows
+        assert ("default", 'flow1') not in processor.flows
         mock_flow1.stop.assert_called_once()
 
-        assert 'flow2' in processor.flows
+        assert ("default", 'flow2') in processor.flows
         mock_flow2.start.assert_called_once()
 
     @with_async_processor_patches