Add monitoring/alerting for new aggregation jobs via src/monitor.rs and src/alerts.rs

[christabel888]

Context: New scheduled jobs (#2, #34, plus the extended contract listener from #20) are new failure surfaces. src/monitor.rs and src/alerts.rs already exist for this kind of thing.

Where:

• src/monitor.rs, src/alerts.rs

What to do:

• Add health checks / alert rules for the new jobs (job hasn't run in N intervals, job erroring repeatedly), following whatever pattern already covers the existing jobs.

Suggested approach:

1. Look at how src/monitor.rs/src/alerts.rs already cover the existing jobs (corridor refresh, anchor refresh, etc.) and add the same shape of health check for Add daily-active-accounts computation job in src/jobs #2's DAA job, Add Soroban contract-invocation ingestion pipeline in src/ingestion #20's extended listener, and Add hourly background job to compute top movers in src/jobs #34's top-movers job.
2. Alert on "hasn't run successfully in N expected intervals" and "erroring repeatedly," not just "is the process running."

Watch out for:

• Alert fatigue is a real risk if thresholds are too tight for jobs with long intervals (e.g. an hourly job) -- calibrate the "hasn't run" threshold to a few missed intervals, not one.

Definition of done:

• New jobs are covered by the same monitoring/alerting as existing jobs, not silently unmonitored