feat: in-process nightly scheduler + pause at window end

Hook registers a 15-minute schedule that starts/resumes the backfill only
inside the maintenance window (no external cron or token). The backfill
pauses when the window closes and resumes next night. UI shows paused
state and last-run errors.

AGENTS.md

@@ -88,6 +88,14 @@ pacing).
 - `state.jsonl` = append-only completed `{file_id,preset_key,format}` → resume.
 - All state is **file-backed** (PM2 cluster, 8 workers — never in-memory).
 
+## Nightly scheduling
+
+- The hook registers `schedule('*/15 * * * *')` — **in-process**, no external cron/token. Every tick it
+  checks enabled + maintenance window + no active run, then starts/resumes the backfill.
+- The backfill **pauses** when the window closes (`run.paused = true`) and resumes next night.
+- `scheduleSynchronizedJob` makes the cron cluster-safe; the `run.lock` file is a second guard.
+- `Run now` in the admin module ignores the window (`ignoreWindow: true`).
+
 ## Gotchas learned the hard way
 
 - **Directus coerces env values**: `"true"` arrives as boolean `true`, `"1"` as number. Env parsing must