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]>

.env.example

@@ -39,6 +39,11 @@ BADGE_UPLOAD_DIR=./public/assets/images/badges
 EMULATOR_JAR_PATH=./emulator/Arcturus.jar
 EMULATOR_BACKUP_DIR=./backups/emulator
 EMULATOR_BACKUP_KEEP=7
+# Optional mysqldump (jobs-worker daily 03:30). Requires mysqldump on PATH.
+DB_BACKUP_DIR=
+DB_BACKUP_KEEP=7
+# Minutes between repeat health-fail alerts from jobs-worker (default 15).
+HEALTH_ALERT_COOLDOWN_MIN=15
 
 # --- RCON (Low Latency Loop) ---
 RCON_HOST=127.0.0.1