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/db_maintenance.py

@@ -21,6 +21,7 @@ from datetime import datetime, timezone
 from sqlalchemy import text
 
 from scribe.models import async_session, engine
+from scribe.models.base import iso
 from scribe.services.settings import get_admin_setting, set_admin_setting
 
 logger = logging.getLogger(__name__)
@@ -128,10 +129,6 @@ _HEALTH_SQL = text("""
 """)
 
 
-def _iso(value) -> str | None:
-    return value.isoformat() if value is not None else None
-
-
 async def get_table_health() -> dict:
     """Per-table health from Postgres statistics + the total database size.
 
@@ -156,8 +153,8 @@ async def get_table_health() -> dict:
             "dead_pct": float(r["dead_pct"] or 0),
             "total_bytes": int(r["total_bytes"] or 0),
             "mod_since_analyze": int(r["mod_since_analyze"] or 0),
-            "last_vacuum": _iso(r["last_vacuum"]),
-            "last_analyze": _iso(r["last_analyze"]),
+            "last_vacuum": iso(r["last_vacuum"]),
+            "last_analyze": iso(r["last_analyze"]),
         }
         for r in rows
     ]