feat(cron): configurable failure alerts for repeated job errors (openclaw#24789) thanks @0xbrak

Verified:
- pnpm install --frozen-lockfile
- pnpm check
- pnpm test -- --run src/cron/service.failure-alert.test.ts src/cli/cron-cli.test.ts src/gateway/protocol/cron-validators.test.ts

Co-authored-by: 0xbrak <181251288+0xbrak@users.noreply.github.com>
Co-authored-by: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>

src/config/types.cron.ts

@@ -10,6 +10,12 @@ export type CronRetryConfig = {
   retryOn?: CronRetryOn[];
 };
 
+export type CronFailureAlertConfig = {
+  enabled?: boolean;
+  after?: number;
+  cooldownMs?: number;
+};
+
 export type CronConfig = {
   enabled?: boolean;
   store?: string;
@@ -37,4 +43,5 @@ export type CronConfig = {
     maxBytes?: number | string;
     keepLines?: number;
   };
+  failureAlert?: CronFailureAlertConfig;
 };