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_graph_rag_integration.py

@@ -146,7 +146,6 @@ class TestGraphRagIntegration:
         # Act
         response = await graph_rag.query(
             query=query,
-            user=user,
             collection=collection,
             entity_limit=entity_limit,
             triple_limit=triple_limit,
@@ -163,7 +162,6 @@ class TestGraphRagIntegration:
         call_args = mock_graph_embeddings_client.query.call_args
         assert call_args.kwargs['vector'] == [[0.1, 0.2, 0.3, 0.4, 0.5]]
         assert call_args.kwargs['limit'] == entity_limit
-        assert call_args.kwargs['user'] == user
         assert call_args.kwargs['collection'] == collection
 
         # 3. Should query triples to build knowledge subgraph
@@ -204,7 +202,6 @@ class TestGraphRagIntegration:
             # Act
             await graph_rag.query(
                 query=query,
-                user="test_user",
                 collection="test_collection",
                 entity_limit=config["entity_limit"],
                 triple_limit=config["triple_limit"]
@@ -224,7 +221,6 @@ class TestGraphRagIntegration:
         with pytest.raises(Exception) as exc_info:
             await graph_rag.query(
                 query="test query",
-                user="test_user",
                 collection="test_collection"
             )
 
@@ -247,7 +243,6 @@ class TestGraphRagIntegration:
         # Act
         response = await graph_rag.query(
             query="unknown topic",
-            user="test_user",
             collection="test_collection",
             explain_callback=collect_provenance
         )
@@ -267,7 +262,6 @@ class TestGraphRagIntegration:
         # First query
         await graph_rag.query(
             query=query,
-            user="test_user",
             collection="test_collection"
         )
 
@@ -277,7 +271,6 @@ class TestGraphRagIntegration:
         # Second identical query
         await graph_rag.query(
             query=query,
-            user="test_user",
             collection="test_collection"
         )
 
@@ -289,26 +282,27 @@ class TestGraphRagIntegration:
         assert second_call_count >= 0  # Should complete without errors
 
     @pytest.mark.asyncio
-    async def test_graph_rag_multi_user_isolation(self, graph_rag, mock_graph_embeddings_client):
-        """Test that different users/collections are properly isolated"""
+    async def test_graph_rag_multi_collection_isolation(self, graph_rag, mock_graph_embeddings_client):
+        """Test that different collections propagate through to the embeddings query.
+
+        Workspace isolation is enforced by flow.workspace at the service
+        boundary — not by parameters on GraphRag.query — so this test
+        verifies collection routing only.
+        """
         # Arrange
         query = "test query"
-        user1, collection1 = "user1", "collection1"
-        user2, collection2 = "user2", "collection2"
+        collection1 = "collection1"
+        collection2 = "collection2"
 
         # Act
-        await graph_rag.query(query=query, user=user1, collection=collection1)
-        await graph_rag.query(query=query, user=user2, collection=collection2)
+        await graph_rag.query(query=query, collection=collection1)
+        await graph_rag.query(query=query, collection=collection2)
 
-        # Assert - Both users should have separate queries
+        # Assert - Each call propagated its collection
         assert mock_graph_embeddings_client.query.call_count == 2
 
-        # Verify first call
         first_call = mock_graph_embeddings_client.query.call_args_list[0]
-        assert first_call.kwargs['user'] == user1
         assert first_call.kwargs['collection'] == collection1
 
-        # Verify second call
         second_call = mock_graph_embeddings_client.query.call_args_list[1]
-        assert second_call.kwargs['user'] == user2
         assert second_call.kwargs['collection'] == collection2