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.

specs/api/paths/flow/agent.yaml

@@ -69,25 +69,21 @@ post:
             summary: Simple question
             value:
               question: What is the capital of France?
-              user: alice
           streamingQuestion:
             summary: Question with streaming enabled
             value:
               question: Explain quantum computing
-              user: alice
               streaming: true
           conversationWithHistory:
             summary: Multi-turn conversation
             value:
               question: And what about its population?
-              user: alice
               history:
                 - thought: User is asking about the capital of France
                   action: search
                   arguments:
                     query: "capital of France"
                   observation: "Paris is the capital of France"
-                  user: alice
   responses:
     '200':
       description: Successful response

specs/api/paths/flow/document-embeddings.yaml

@@ -75,7 +75,6 @@ post:
             value:
               vectors: [0.023, -0.142, 0.089, 0.234, -0.067, 0.156, 0.201, -0.178]
               limit: 10
-              user: alice
               collection: research
           largeQuery:
             summary: Larger result set

specs/api/paths/flow/document-load.yaml

@@ -88,14 +88,12 @@ post:
             value:
               data: JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2cvUGFnZXMgMiAwIFI+PmVuZG9iagoyIDAgb2JqCjw8L1R5cGUvUGFnZXMvS2lkc1szIDAgUl0vQ291bnQgMT4+ZW5kb2JqCg==
               id: doc-789
-              user: alice
               collection: research
           withMetadata:
             summary: Load with metadata
             value:
               data: JVBERi0xLjQKJeLjz9MK...
               id: doc-101112
-              user: bob
               collection: papers
               metadata:
                 - s: {v: "doc-101112", e: false}

specs/api/paths/flow/document-rag.yaml

@@ -40,7 +40,6 @@ post:
       - Higher = more context but slower
       - Lower = faster but may miss relevant info
     - **collection**: Target specific document collection
-    - **user**: Multi-tenant isolation
 
   operationId: documentRagService
   security:
@@ -64,13 +63,11 @@ post:
             summary: Basic document query
             value:
               query: What are the key findings in the research papers?
-              user: alice
               collection: research
           streamingQuery:
             summary: Streaming query
             value:
               query: Summarize the main conclusions
-              user: alice
               collection: research
               doc-limit: 15
               streaming: true

specs/api/paths/flow/graph-embeddings.yaml

@@ -66,7 +66,6 @@ post:
             value:
               vectors: [0.023, -0.142, 0.089, 0.234, -0.067, 0.156, 0.201, -0.178]
               limit: 10
-              user: alice
               collection: research
           largeQuery:
             summary: Larger result set

specs/api/paths/flow/graph-rag.yaml

@@ -77,13 +77,11 @@ post:
             summary: Basic graph query
             value:
               query: What connections exist between quantum physics and computer science?
-              user: alice
               collection: research
           streamingQuery:
             summary: Streaming query with custom limits
             value:
               query: Trace the historical development of AI from Turing to modern LLMs
-              user: alice
               collection: research
               entity-limit: 40
               triple-limit: 25

specs/api/paths/flow/row-embeddings.yaml

@@ -62,7 +62,6 @@ post:
               vectors: [0.023, -0.142, 0.089, 0.234, -0.067, 0.156, 0.201, -0.178]
               schema_name: customers
               limit: 10
-              user: alice
               collection: sales
           filteredQuery:
             summary: Search specific index

specs/api/paths/flow/rows.yaml

@@ -89,7 +89,6 @@ post:
                     email
                   }
                 }
-              user: alice
               collection: research
           queryWithVariables:
             summary: Query with variables

specs/api/paths/flow/sparql-query.yaml

@@ -61,10 +61,6 @@ post:
             query:
               type: string
               description: SPARQL 1.1 query string
-            user:
-              type: string
-              default: trustgraph
-              description: User/keyspace identifier
             collection:
               type: string
               default: default
@@ -78,7 +74,6 @@ post:
             summary: SELECT query
             value:
               query: "SELECT ?s ?p ?o WHERE { ?s ?p ?o } LIMIT 10"
-              user: trustgraph
               collection: default
           askQuery:
             summary: ASK query

specs/api/paths/flow/structured-query.yaml

@@ -79,13 +79,11 @@ post:
             summary: Simple relationship question
             value:
               question: Who does Alice know?
-              user: alice
               collection: research
           complexQuestion:
             summary: Complex multi-hop question
             value:
               question: What companies employ engineers that Bob collaborates with?
-              user: bob
               collection: work
           filterQuestion:
             summary: Question with implicit filters

specs/api/paths/flow/text-load.yaml

@@ -87,14 +87,12 @@ post:
             value:
               text: This is the document text...
               id: doc-123
-              user: alice
               collection: research
           withMetadata:
             summary: Load with RDF metadata using base64 text
             value:
               text: UXVhbnR1bSBjb21wdXRpbmcgdXNlcyBxdWFudHVtIG1lY2hhbmljcyBwcmluY2lwbGVzLi4u
               id: doc-456
-              user: alice
               collection: research
               metadata:
                 - s: {v: "doc-456", e: false}

specs/api/paths/flow/triples.yaml

@@ -81,7 +81,6 @@ post:
               s:
                 v: https://example.com/person/alice
                 e: true
-              user: alice
               collection: research
               limit: 100
           allInstancesOfType:
@@ -100,7 +99,6 @@ post:
               p:
                 v: https://example.com/knows
                 e: true
-              user: alice
               limit: 200
   responses:
     '200':