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_cores/test_knowledge_manager.py

@@ -28,10 +28,12 @@ def mock_flow_config():
     """Mock flow configuration."""
     mock_config = Mock()
     mock_config.flows = {
-        "test-flow": {
-            "interfaces": {
-                "triples-store": {"flow": "test-triples-queue"},
-                "graph-embeddings-store": {"flow": "test-ge-queue"}
+        "test-user": {
+            "test-flow": {
+                "interfaces": {
+                    "triples-store": {"flow": "test-triples-queue"},
+                    "graph-embeddings-store": {"flow": "test-ge-queue"}
+                }
             }
         }
     }
@@ -43,7 +45,7 @@ def mock_flow_config():
 def mock_request():
     """Mock knowledge load request."""
     request = Mock()
-    request.user = "test-user"
+    request.workspace = "test-user"
     request.id = "test-doc-id"
     request.collection = "test-collection"
     request.flow = "test-flow"
@@ -71,7 +73,6 @@ def sample_triples():
     return Triples(
         metadata=Metadata(
             id="test-doc-id",
-            user="test-user",
             collection="default",  # This should be overridden
         ),
         triples=[
@@ -90,7 +91,6 @@ def sample_graph_embeddings():
     return GraphEmbeddings(
         metadata=Metadata(
             id="test-doc-id",
-            user="test-user",
             collection="default",  # This should be overridden
         ),
         entities=[
@@ -146,7 +146,6 @@ class TestKnowledgeManagerLoadCore:
             mock_triples_pub.send.assert_called_once()
             sent_triples = mock_triples_pub.send.call_args[0][1]
             assert sent_triples.metadata.collection == "test-collection"
-            assert sent_triples.metadata.user == "test-user"
             assert sent_triples.metadata.id == "test-doc-id"
 
     @pytest.mark.asyncio
@@ -185,7 +184,6 @@ class TestKnowledgeManagerLoadCore:
             mock_ge_pub.send.assert_called_once()
             sent_ge = mock_ge_pub.send.call_args[0][1] 
             assert sent_ge.metadata.collection == "test-collection"
-            assert sent_ge.metadata.user == "test-user"
             assert sent_ge.metadata.id == "test-doc-id"
 
     @pytest.mark.asyncio 
@@ -193,7 +191,7 @@ class TestKnowledgeManagerLoadCore:
         """Test that load_kg_core falls back to 'default' when request.collection is None."""
         # Create request with None collection
         mock_request = Mock()
-        mock_request.user = "test-user"
+        mock_request.workspace = "test-user"
         mock_request.id = "test-doc-id"
         mock_request.collection = None  # Should fall back to "default"
         mock_request.flow = "test-flow"
@@ -269,7 +267,7 @@ class TestKnowledgeManagerLoadCore:
         """Test that load_kg_core validates flow configuration before processing."""
         # Request with invalid flow
         mock_request = Mock()
-        mock_request.user = "test-user"
+        mock_request.workspace = "test-user"
         mock_request.id = "test-doc-id"
         mock_request.collection = "test-collection"
         mock_request.flow = "invalid-flow"  # Not in mock_flow_config.flows
@@ -297,7 +295,7 @@ class TestKnowledgeManagerLoadCore:
         
         # Test missing ID
         mock_request = Mock()
-        mock_request.user = "test-user"
+        mock_request.workspace = "test-user"
         mock_request.id = None  # Missing
         mock_request.collection = "test-collection"
         mock_request.flow = "test-flow"
@@ -323,7 +321,7 @@ class TestKnowledgeManagerOtherMethods:
     async def test_get_kg_core_preserves_collection_from_store(self, knowledge_manager, sample_triples):
         """Test that get_kg_core preserves collection field from stored data."""
         mock_request = Mock()
-        mock_request.user = "test-user"
+        mock_request.workspace = "test-user"
         mock_request.id = "test-doc-id"
         
         mock_respond = AsyncMock()
@@ -354,7 +352,7 @@ class TestKnowledgeManagerOtherMethods:
     async def test_list_kg_cores(self, knowledge_manager):
         """Test listing knowledge cores."""
         mock_request = Mock()
-        mock_request.user = "test-user"
+        mock_request.workspace = "test-user"
         
         mock_respond = AsyncMock()
         
@@ -376,7 +374,7 @@ class TestKnowledgeManagerOtherMethods:
     async def test_delete_kg_core(self, knowledge_manager):
         """Test deleting knowledge cores."""
         mock_request = Mock()
-        mock_request.user = "test-user"
+        mock_request.workspace = "test-user"
         mock_request.id = "test-doc-id"
         
         mock_respond = AsyncMock()