Infer daily statistics failures from expected podcasts

[mre]

Summary

• Fill all 90 daily bars by treating every podcast ever seen for an endpoint as expected each day.
• Infer daily failures from missing successful updates instead of showing grey no-data bars.
• Remove first-seen/grey-bar logic and the extra first-update query.
• Keep a code comment documenting that updates only records successful imports.

Note

This intentionally treats missing successful updates as failures for dashboard purposes. That matches the rule that active podcasts are expected to run every endpoint daily, but it is still inferred from successes rather than explicit failure records.

Validation

• npx jest src/api/StatusApi.test.ts src/db/StatusRepository.test.ts --runInBand
• npm run build
• npm run lint