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_extract/test_streaming_triples/test_definitions_batching.py

@@ -34,11 +34,10 @@ def _make_defn(entity, definition):
     return {"entity": entity, "definition": definition}
 
 
-def _make_chunk_msg(text, meta_id="chunk-1", root="root-1",
-                    user="user-1", collection="col-1", document_id=""):
+def _make_chunk_msg(text, meta_id="chunk-1", root="root-1", collection="col-1", document_id=""):
     chunk = Chunk(
         metadata=Metadata(
-            id=meta_id, root=root, user=user, collection=collection,
+            id=meta_id, root=root, collection=collection,
         ),
         chunk=text.encode("utf-8"),
         document_id=document_id,
@@ -229,8 +228,7 @@ class TestMetadataPreservation:
         defs = [_make_defn("X", "def X")]
         flow, triples_pub, _, _ = _make_flow(defs)
         msg = _make_chunk_msg(
-            "text", meta_id="c-1", root="r-1",
-            user="u-1", collection="coll-1",
+            "text", meta_id="c-1", root="r-1", collection="coll-1",
         )
 
         await proc.on_message(msg, MagicMock(), flow)
@@ -238,7 +236,6 @@ class TestMetadataPreservation:
         for triples_msg in _sent_triples(triples_pub):
             assert triples_msg.metadata.id == "c-1"
             assert triples_msg.metadata.root == "r-1"
-            assert triples_msg.metadata.user == "u-1"
             assert triples_msg.metadata.collection == "coll-1"
 
     @pytest.mark.asyncio
@@ -247,8 +244,7 @@ class TestMetadataPreservation:
         defs = [_make_defn("X", "def X")]
         flow, _, ecs_pub, _ = _make_flow(defs)
         msg = _make_chunk_msg(
-            "text", meta_id="c-2", root="r-2",
-            user="u-2", collection="coll-2",
+            "text", meta_id="c-2", root="r-2", collection="coll-2",
         )
 
         await proc.on_message(msg, MagicMock(), flow)

tests/unit/test_extract/test_streaming_triples/test_relationships_batching.py

@@ -38,12 +38,11 @@ def _make_rel(subject, predicate, obj, object_entity=True):
     }
 
 
-def _make_chunk_msg(text, meta_id="chunk-1", root="root-1",
-                    user="user-1", collection="col-1", document_id=""):
+def _make_chunk_msg(text, meta_id="chunk-1", root="root-1", collection="col-1", document_id=""):
     """Build a mock message wrapping a Chunk."""
     chunk = Chunk(
         metadata=Metadata(
-            id=meta_id, root=root, user=user, collection=collection,
+            id=meta_id, root=root, collection=collection,
         ),
         chunk=text.encode("utf-8"),
         document_id=document_id,
@@ -189,8 +188,7 @@ class TestMetadataPreservation:
         rels = [_make_rel("X", "rel", "Y")]
         flow, pub, _ = _make_flow(rels)
         msg = _make_chunk_msg(
-            "text", meta_id="c-1", root="r-1",
-            user="u-1", collection="coll-1",
+            "text", meta_id="c-1", root="r-1", collection="coll-1",
         )
 
         await proc.on_message(msg, MagicMock(), flow)
@@ -198,7 +196,6 @@ class TestMetadataPreservation:
         for triples_msg in _sent_triples(pub):
             assert triples_msg.metadata.id == "c-1"
             assert triples_msg.metadata.root == "r-1"
-            assert triples_msg.metadata.user == "u-1"
             assert triples_msg.metadata.collection == "coll-1"