refactor(services): one periodic-task shape, one APScheduler job shape, one token hash, one summary rule — the services pass of the shape audit (#2830, milestone 296)

- background.start_periodic(interval, work, label=) replaces the three hand-rolled
  while-True/sleep/try loops in logging, auth and notifications.
- services/scheduler.ScheduledJob replaces the four private BackgroundScheduler
  copies in recurrence/version_pinning/trash/db_maintenance schedulers; public
  start_/stop_/reschedule_ surfaces unchanged.
- api_keys.hash_token is the one sha256 helper; auth.py used to inline it 5x.
- auth.is_registration_open reads via settings.get_admin_setting; notification
  prefs read via settings.get_setting; _fire_share_email uses _get_user_email.
- projects.get_project_summary / milestones.get_project_milestone_summary are
  now the one-id view of their batch siblings instead of a second copy of the
  queries; sharing.best_permission_by (was _deduplicate_by_permission) is the
  one rank-dedup, now also used by list_projects_for_user.
- backup: the row builders for every section both exporters carry are named
  functions, so a column added to one export cannot silently miss the other.
- iso() from models.base replaces the attr.isoformat()-if-attr-else-None idiom
  and db_maintenance._iso across services; backup keeps its explicit shape.
- trash.py hoists the sql_delete/timedelta imports it re-imported per function.

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

src/scribe/services/milestones.py

@@ -235,12 +235,6 @@ async def get_project_milestone_summaries(
 
 
 async def get_project_milestone_summary(user_id: int, project_id: int) -> list[dict]:
-    """Return ordered list of milestones with their progress stats."""
-    milestones = await list_milestones(user_id, project_id)
-    result = []
-    for m in milestones:
-        progress = await get_milestone_progress(m.id)
-        entry = m.to_dict()
-        entry.update(progress)
-        result.append(entry)
-    return result
+    """Ordered milestones with progress — the one-project view of
+    get_project_milestone_summaries (two queries, not N+1)."""
+    return (await get_project_milestone_summaries(user_id, [project_id])).get(project_id, [])