fix(harvest): reprobe newly-discovered slugs on the next pass

[datascry]

Fixes why the connectors onboarded this month show only a handful of live jobs. Not a parser bug — the connectors work (jibeapply's 3 seeds = 3,352 jobs exactly; live-probing 25 random discovered hireology slugs gives 16×200 / 9×404, so they're real).

Root cause

Discovery's skip-probe path recorded a brand-new, never-probed slug as transient_failure with last_probed_at = now. The reprobe (--max-age-days default 7) only revisits rows older than the cutoff, so a never-probed slug looked freshly probed and sat unprobed for a full week — invisible to reprobe (too fresh) and scrape (only takes status==live). Every new connector's reprobe logged 0 tenants older than 7 days; nothing to do. The "fat" connectors (careerplug 6,376 jobs, jibeapply 3,352) just have high-volume seeds; the "thin" ones (hireology 12, isolvedhire 11) have small seeds — same underlying state, thousands of real tenants stuck in limbo.

Fix

1. Code (runner.ts): stamp new skip-probe slugs with an epoch last_probed_at sentinel (1970-01-01T00:00:00.000Z, matching the sitemap backend's convention) so the next reprobe includes them immediately. first_seen_at stays the real discovery day. New runner.test.ts assertion.
2. Backlog backfill: reset last_probed_at to epoch on the 14,234 unprobed transient_failure rows of the six affected connectors (careerplug/jibeapply/isolvedhire/applitrack/hiringthing/hireology) so the next reprobe promotes the live ones now instead of waiting out the window. Byte-verified: only last_probed_at changed, only on transient_failure rows, live/dead untouched, all schema-valid.

Safety (adversarially verified)

• Reprobe has no age-based drop path — it filters stale → sorts oldest-first → probes → updates; every tenant is preserved. Epoch rows are probed, never dropped.
• --stale-ttl-days drops job rows by last_seen_at, a different entity — can't drop a tenant.
• Incident guard only counts previously-live rows; epoch rows are transient_failure, so they can't trip/suppress it.
• No starvation: each connector's epoch count is under the 5,000 batch cap (drains in one run), and probed rows re-stamp to now, strictly shrinking the stale set.

Gates

bun run test 1656 pass · typecheck · lint clean. Adversarial review: SHIP (no Critical/Major/Minor).

Follow-up after merge: dispatch weekly-harvest mode=reprobe-only to promote the freed tenants; the thin connectors should climb into the thousands.