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>

apps/api/src/auth/abilities.ts

@@ -40,7 +40,8 @@ export type Ability =
   | "lookup:manage"
   | "user:manage"
   | "db:manage"
-  | "notification:send";
+  | "notification:send"
+  | "setting:manage";
 
 /** Minimum role required for each ability. */
 export const ABILITY_MIN: Record<Ability, Role> = {
@@ -79,6 +80,10 @@ export const ABILITY_MIN: Record<Ability, Role> = {
   // a STAFF user typing one customer receipt is fine; a STAFF user firing
   // 260 mail merges on the customer base is not.
   "notification:send": "MANAGER",
+  // Editing operator configuration. Above `notification:send` on purpose:
+  // firing a sweep is the day job, but changing WHERE the audit summaries
+  // land is how someone would quietly stop them being read.
+  "setting:manage": "ADMIN",
 };
 
 export const ALL_ABILITIES = Object.keys(ABILITY_MIN) as Ability[];