Add systemd timer deployment for scheduled ingestion cycle

- deploy/goodnews.service: oneshot unit running 'goodnews cycle' with a
  generous TimeoutStartSec so long classify runs are not killed.
- deploy/goodnews.timer: every 15 min, Persistent=true to catch missed runs.
- deploy/goodnews.env.example: LLM endpoint + DB path for the scheduled run.
- README: scheduling/install docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -104,6 +104,36 @@ docker run -p 8000:8000 -v /srv/goodnews/data:/data goodnews
 `GOODNEWS_DB` controls the database path (defaults to `data/goodnews.sqlite3`).
 Put a reverse proxy (Caddy/nginx) in front for TLS once a domain is attached.
 
+## Scheduling
+
+A single idempotent command runs the whole pipeline and is safe to invoke as
+often as you like — it only polls sources that are *due* (per each source's
+`poll_interval_minutes`), only classifies articles the model hasn't seen, and
+rebuilds the current day's brief:
+
+```bash
+python3 -m goodnews cycle                 # poll due -> classify new -> rebuild today's brief
+python3 -m goodnews cycle --force         # poll every active source regardless of interval
+python3 -m goodnews cycle --no-classify   # skip the LLM step (e.g. model box offline)
+```
+
+A systemd timer runs it every 15 minutes. Unit files live in `deploy/`:
+
+```bash
+sudo install -d /etc/goodnews
+sudo install -m 644 deploy/goodnews.env.example /etc/goodnews/goodnews.env  # then edit
+sudo install -m 644 deploy/goodnews.service deploy/goodnews.timer /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable --now goodnews.timer
+
+systemctl list-timers goodnews.timer          # when it next runs
+journalctl -u goodnews.service -f             # watch cycle output
+```
+
+`/etc/goodnews/goodnews.env` supplies `GOODNEWS_LLM_BASE_URL`, `GOODNEWS_LLM_MODEL`,
+and `GOODNEWS_DB` to the scheduled run. The timer uses `Persistent=true`, so a
+run missed while the machine was off is caught up on the next boot.
+
 ## Next Steps
 
 1. Run the poller for a few days and inspect which sources produce useful candidates.