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_translators/test_document_embeddings_translator_roundtrip.py

@@ -30,7 +30,6 @@ def sample():
         metadata=Metadata(
             id="doc-1",
             root="",
-            user="alice",
             collection="testcoll",
         ),
         chunks=[
@@ -56,7 +55,6 @@ class TestDocumentEmbeddingsTranslator:
         assert isinstance(decoded, DocumentEmbeddings)
         assert isinstance(decoded.metadata, Metadata)
         assert decoded.metadata.id == "doc-1"
-        assert decoded.metadata.user == "alice"
         assert decoded.metadata.collection == "testcoll"
 
         assert len(decoded.chunks) == 2

tests/unit/test_translators/test_knowledge_translator_roundtrip.py

@@ -41,7 +41,7 @@ def translator():
 def graph_embeddings_request():
     return KnowledgeRequest(
         operation="put-kg-core",
-        user="alice",
+        workspace="alice",
         id="doc-1",
         flow="default",
         collection="testcoll",
@@ -49,7 +49,6 @@ def graph_embeddings_request():
             metadata=Metadata(
                 id="doc-1",
                 root="",
-                user="alice",
                 collection="testcoll",
             ),
             entities=[
@@ -70,7 +69,6 @@ def graph_embeddings_request():
 def triples_request():
     return KnowledgeRequest(
         operation="put-kg-core",
-        user="alice",
         id="doc-1",
         flow="default",
         collection="testcoll",
@@ -78,7 +76,6 @@ def triples_request():
             metadata=Metadata(
                 id="doc-1",
                 root="",
-                user="alice",
                 collection="testcoll",
             ),
             triples=[
@@ -113,7 +110,7 @@ class TestKnowledgeRequestTranslatorGraphEmbeddings:
 
         assert isinstance(decoded, KnowledgeRequest)
         assert decoded.operation == "put-kg-core"
-        assert decoded.user == "alice"
+        assert decoded.workspace == "alice"
         assert decoded.id == "doc-1"
         assert decoded.flow == "default"
         assert decoded.collection == "testcoll"
@@ -123,7 +120,6 @@ class TestKnowledgeRequestTranslatorGraphEmbeddings:
         assert isinstance(ge, GraphEmbeddings)
         assert isinstance(ge.metadata, Metadata)
         assert ge.metadata.id == "doc-1"
-        assert ge.metadata.user == "alice"
         assert ge.metadata.collection == "testcoll"
 
         assert len(ge.entities) == 2
@@ -143,7 +139,6 @@ class TestKnowledgeRequestTranslatorTriples:
         assert decoded.triples is not None
         assert isinstance(decoded.triples.metadata, Metadata)
         assert decoded.triples.metadata.id == "doc-1"
-        assert decoded.triples.metadata.user == "alice"
         assert decoded.triples.metadata.collection == "testcoll"
 
         assert len(decoded.triples.triples) == 1