Add ThresholdScanJob for firehose virality webhook firing
Scheduled queue job that scans like_counts_daily for posts at or above
the 1k / 10k like thresholds, enriches them via the AppView, and fires
a Discord webhook the first time each post crosses each threshold.
Dedup is stored in SQLite notified_thresholds so a given (post, threshold)
only fires once. Deleted posts / accounts silently insert a dedup row so
they're not re-enriched on every poll. AppView failures (network / 5xx)
capture to PostHog and retry on the next tick. Webhook HTTP failures
after the retry budget also capture to PostHog but still insert the
dedup row to prevent an unbounded retry loop against a broken URL.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>