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/knowledge.py

@@ -22,6 +22,7 @@ from sqlalchemy import and_, func, or_, select
 
 from scribe.models import async_session
 from scribe.models.note import Note
+from scribe.models.base import iso
 from scribe.services.access import browsable_notes_clause, readable_notes_clause
 
 logger = logging.getLogger(__name__)
@@ -211,8 +212,8 @@ def _note_to_item(note: Note) -> dict:
         # These lists now include records shared with the caller, so the client
         # needs the owner to tell "mine" from "someone else's" in a mixed list.
         "user_id": note.user_id,
-        "created_at": note.created_at.isoformat(),
-        "updated_at": note.updated_at.isoformat(),
+        "created_at": iso(note.created_at),
+        "updated_at": iso(note.updated_at),
     }
     # Drift verdict (#2086), when one has been recorded. Included here rather
     # than decorated on by the snippet layer because `current` is derivable from
@@ -249,7 +250,7 @@ def _note_to_item(note: Note) -> dict:
         item["task_kind"] = note.task_kind
         item["status"] = note.status
         item["priority"] = note.priority
-        item["due_date"] = note.due_date.isoformat() if note.due_date else None
+        item["due_date"] = iso(note.due_date)
 
     return item