api: pause spam check when IPQualityScore credits run out

SD2 (14 §3): out of credits pauses IPQualityScore (one warning, one
event), the FTC list answers meanwhile, the dashboard shows a dismissable
spam_quota warning, and spamQuotaCheck resumes it every 6 hours once
credits are back. A newly saved key resumes it at once.

Follow-up: confirm with the owner's real key that the Credit Usage API
costs no credit (TODO in 14 §2.1).

packages/shared/src/settings.ts

@@ -348,7 +348,8 @@ export type AiTestResult =
   { ok: true; ms: number; detail: string; audio?: string } | { ok: false; error: string };
 
 /** GET /api/system/warnings: shown as the dashboard banner (05 §2). */
-export type Warning = { code: string; message: string; link: string };
+/** `dismissable`: POST /api/system/warnings/{code}/dismiss hides it (14 §3). */
+export type Warning = { code: string; message: string; link: string; dismissable?: boolean };
 
 /** GET /api/system/backups (04 §8.1). */
 export type BackupDto = { name: string; size: number; createdAt: string };