refactor(tests): per-model fakes, FakeMCP and session mocks come from tests/helpers (#2825, milestone 296 area 1, batch 2)

Second pass over the tests/ ledger after bbee0d0. fake_record(**attrs) is the
one MagicMock-with-real-attributes builder (to_dict mirrors them; the
note-2109 hazard documented once); fake_note/fake_task/fake_snippet/
fake_project/fake_milestone/fake_system/fake_rulebook/fake_topic/fake_rule
carry each model's ordinary defaults on top of it, replacing 14 per-file
factories (two rulebook trios in tool-vs-service wordings, _fake_task, _fake_ms,
_fake_project, _plan_note, _fake_snippet, two _snippet adapters now one-liners
over fake_snippet). FakeMCP replaces the five closure-over-a-list registrar
fakes (+ _Recorder); loc() and design_token_stub() replace the paired _loc /
_token / _T stand-ins; every hand-built async_session mock (9 helper defs and
14 inline copies) now starts from make_mock_session(). Call sites rewritten by
AST with each file's former defaults made explicit, so behaviour is unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_shared_provenance.py

@@ -9,14 +9,13 @@ passive surface Scribe has (each entry becomes an auto-surfacing skill file).
 from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
+from tests.helpers import make_mock_session
 
 
 def _session_returning_rows(rows):
     result = MagicMock()
     result.all.return_value = rows
-    session = AsyncMock()
-    session.__aenter__ = AsyncMock(return_value=session)
-    session.__aexit__ = AsyncMock(return_value=False)
+    session = make_mock_session()
     session.execute = AsyncMock(return_value=result)
     return session
 
@@ -62,9 +61,7 @@ async def test_provenance_names_the_owner_and_permission():
     from scribe.services.access import describe_provenance
     note = MagicMock(id=1, user_id=9)
     owner = MagicMock(username="alex")
-    session = AsyncMock()
-    session.__aenter__ = AsyncMock(return_value=session)
-    session.__aexit__ = AsyncMock(return_value=False)
+    session = make_mock_session()
     session.get = AsyncMock(return_value=owner)
     with patch("scribe.services.access.async_session") as cls, \
          patch("scribe.services.access.get_note_permission",