fix(mcp): list tools return rows that say what a record is, not what it says (#4061)

list_tasks returned every row's to_dict(), body included: a project's todo list
came to 93-165k characters, past what an MCP client accepts inline, so the list
arrived as a file to page through (the #4045 failure, one call over).

- notes.brief_row: id, title, type, project, tags, updated_at; for tasks,
  status, kind, priority, milestone id and title; description, parent and due
  date only when set.
- milestones.titles_for: one query for the milestone titles a page of rows
  names.
- Brief rows on list_tasks, list_notes, get_milestone's steps, get_system and
  list_system_records. get_task / get_note / get_snippet read a record in full,
  and each docstring says so.
- tests/test_list_rows_brief.py pins the ceiling: 100 rows of ~5k-character
  step plans stay under 40k characters.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01821k5B3Ysecp9fNYs92Kuy

tests/test_mcp_tool_tasks.py

@@ -16,7 +16,7 @@ pytestmark = pytest.mark.usefixtures("_bind_user")
 
 @pytest.mark.asyncio
 async def test_list_tasks_passes_is_task_true_and_repackages():
-    rows = [fake_task(id=1), fake_task(id=2)]
+    rows = [fake_task(id=1, milestone_id=None), fake_task(id=2, milestone_id=None)]
     mock = AsyncMock(return_value=(rows, 2))
     with patch("scribe.mcp.tools.tasks.notes_svc.list_notes", mock):
         out = await list_tasks()