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

src/scribe/services/milestones.py

@@ -72,6 +72,26 @@ async def get_milestone(user_id: int, milestone_id: int) -> Milestone | None:
         return result.scalars().first()
 
 
+async def titles_for(milestone_ids: set[int]) -> dict[int, str]:
+    """{id: title} for the given milestones, for rows that name where a record sits.
+
+    No ownership filter, deliberately: the callers are listings whose rows the
+    caller could already read, and a milestone title is part of "where does
+    this record sit". Filtering here would blank the placement of a shared
+    task in someone else's plan while still showing the task.
+    """
+    ids = {i for i in milestone_ids if i}
+    if not ids:
+        return {}
+    async with async_session() as session:
+        rows = (await session.execute(
+            select(Milestone.id, Milestone.title).where(
+                Milestone.id.in_(ids), Milestone.deleted_at.is_(None),
+            )
+        )).all()
+    return {mid: title for mid, title in rows}
+
+
 async def get_milestone_in_project(project_id: int, milestone_id: int) -> Milestone | None:
     """Fetch a milestone by id within a project, without a user_id ownership check.
     Callers must verify project access separately before using this."""