docs: per-source cadence + source-health log + UI (scheduler)

docs/HANDOFF.md

@@ -191,6 +191,7 @@ engine per the user's description. Confirmed decisions:
 ### Honest scope / limitations
 - Current on-disk data has **no factor vintages / Siamchart manifest** → strict event backtest is blocked on real data until collection accumulates (this is the intended fail-closed behavior, matching "strict PIT or block").
 - **Auto-collection is now live** (commit `1fb1e1a`): the scheduler writes PIT factor + Siamchart vintages every refresh on whichever machine the app runs, so strict runs become ready once enough data is knowable. Because `released_at=retrieved_at=now`, `ready=true` currently requires an explicit `end=today` window (auto end=yesterday stays blocked until real history accumulates — honest, no assumed reporting lag).
+- **Per-source cadence + source health** (commit `14b2aef`): slow factors refresh monthly/quarterly (cooldown markers), prices + Siamchart daily; every refresh logs per-source outcome to `data/scheduler/source_health.json`, auto-classified (network/timeout/http/parse/structure/auth), shown in the "สถานะข้อมูล" panel with one-click copy of the cause.
 - Dividend payment timing is the confirmed `ex_date + 30d` **assumption** (Siamchart gives ex-date+DPS, not pay date); every result exposes `dividend_timing=ex_date_plus_30d`.
 - Only the new `/api/v1/backtest/run` route is event-driven/strict; the legacy `POST /api/v1/backtest` remains as the descriptive non-PIT path.