feat(notificaciones): edit summary recipients in the UI

NOTIFICATION_ADMIN_EMAILS made "add Beto to the summaries" a redeploy —
the wrong unit of work for a list that changes when office staff change.

Adds `app_settings`, a key/value table for the configuration staff must
be able to change without a deploy, and `SettingsService`, which resolves
every key db -> env -> default and reports which of the three a value
came from. That ladder is what makes the move safe: a deployment behaves
exactly as before until somebody saves in the UI, and the screen can say
"this is still coming from the deployment" rather than implying somebody
chose it.

- new ability `setting:manage` (ADMIN) — deliberately above
  `notification:send`, since redirecting the audit summaries is how
  someone would quietly stop them being read
- GET/PUT /notifications/settings/admin-emails; read is open to any
  logged-in user so the UI can display the list, write is gated
- resolved per job, not cached at boot, or we would reintroduce exactly
  the restart-to-apply behaviour being removed
- a saved empty list means "nobody" and does NOT fall through to the env,
  or clearing the field would keep mailing the people just removed

Credentials stay in env — see the model doc for where the line is drawn.

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

deploy/jorgecuadros-app.env.example

@@ -56,6 +56,8 @@ SES_SECRET_KEY=
 # Optional — only needed to publish bounce/complaint events.
 SES_CONFIGURATION_SET=
 
-# Recipients of the per-job summary email. Comma-separated; unset falls back to
-# the defaults in NotificationsService.
+# Recipients of the per-job summary email. NOW EDITABLE IN THE UI
+# (/notificaciones > Servicios > "Destinatarios del resumen", ADMIN only), so
+# this is only the fallback for a deployment where nobody has set it there.
+# A saved value takes precedence and this var is ignored from then on.
 NOTIFICATION_ADMIN_EMAILS=rmancinas@freakma.net,mpulido@freakma.net