feat(ops): health-fail alerts, optional DB backup, admin UX polish

Wire jobs-worker health probes to Discord/email alerts with cooldown, optional mysqldump, rate-limit /api/health, mark-all-read alerts, ConfirmDialog on destructive admin actions, and raise coverage floors.

Co-authored-by: Cursor <[email protected]>

vitest.config.ts

@@ -24,10 +24,10 @@ export default defineConfig({
 			provider: "v8",
 			reporter: ["text", "lcov", "html"],
 			thresholds: {
-				statements: 6,
-				branches: 4,
-				functions: 5,
-				lines: 6,
+				statements: 7,
+				branches: 5,
+				functions: 6,
+				lines: 7,
 			},
 			include: ["src/**/*.{ts,tsx}"],
 			exclude: [