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_agent/test_tool_service.py

@@ -167,39 +167,28 @@ class TestToolServiceRequest:
     """Test cases for tool service request format"""
 
     def test_request_format(self):
-        """Test that request is properly formatted with user, config, and arguments"""
-        # Arrange
-        user = "alice"
+        """Test that request is properly formatted with config and arguments"""
         config_values = {"style": "pun", "collection": "jokes"}
         arguments = {"topic": "programming"}
 
-        # Act - simulate request building
         request = {
-            "user": user,
             "config": json.dumps(config_values),
             "arguments": json.dumps(arguments)
         }
 
-        # Assert
-        assert request["user"] == "alice"
         assert json.loads(request["config"]) == {"style": "pun", "collection": "jokes"}
         assert json.loads(request["arguments"]) == {"topic": "programming"}
 
     def test_request_with_empty_config(self):
         """Test request when no config values are provided"""
-        # Arrange
-        user = "bob"
         config_values = {}
         arguments = {"query": "test"}
 
-        # Act
         request = {
-            "user": user,
             "config": json.dumps(config_values) if config_values else "{}",
             "arguments": json.dumps(arguments) if arguments else "{}"
         }
 
-        # Assert
         assert request["config"] == "{}"
         assert json.loads(request["arguments"]) == {"query": "test"}
 
@@ -386,18 +375,13 @@ class TestJokeServiceLogic:
         assert map_topic_to_category("random topic") == "default"
         assert map_topic_to_category("") == "default"
 
-    def test_joke_response_personalization(self):
-        """Test that joke responses include user personalization"""
-        # Arrange
-        user = "alice"
+    def test_joke_response_format(self):
+        """Test that joke response is formatted as expected"""
         style = "pun"
         joke = "Why do programmers prefer dark mode? Because light attracts bugs!"
 
-        # Act
-        response = f"Hey {user}! Here's a {style} for you:\n\n{joke}"
+        response = f"Here's a {style} for you:\n\n{joke}"
 
-        # Assert
-        assert "Hey alice!" in response
         assert "pun" in response
         assert joke in response
 
@@ -439,20 +423,14 @@ class TestDynamicToolServiceBase:
 
     def test_request_parsing(self):
         """Test parsing of incoming request"""
-        # Arrange
         request_data = {
-            "user": "alice",
             "config": '{"style": "pun"}',
             "arguments": '{"topic": "programming"}'
         }
 
-        # Act
-        user = request_data.get("user", "trustgraph")
         config = json.loads(request_data["config"]) if request_data["config"] else {}
         arguments = json.loads(request_data["arguments"]) if request_data["arguments"] else {}
 
-        # Assert
-        assert user == "alice"
         assert config == {"style": "pun"}
         assert arguments == {"topic": "programming"}