fix: address final-review findings on the latest-chapter poller

Wires the five poll env vars into docker-compose (the documented kill
switch was inert), skips fetching unknown sites and non-https URLs
before spending a request, and makes runOnce's summary log fire on
empty and cancelled ticks. Records the accepted non-atomic Get+Upsert
window and the one-interval startup delay in the docs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.env.example

@@ -45,6 +45,10 @@ WEB_PASSWORD=
 # LATEST_CHAPTER_POLL_BATCH=14        # series per wake
 # LATEST_CHAPTER_POLL_STAGGER=20s     # delay between fetches in a batch
 #
+# Uses a ticker, not an immediate first run: the first poll happens one
+# INTERVAL after startup, not at startup. A container restarting more often
+# than INTERVAL never polls.
+#
 # BATCH x (COOLDOWN / INTERVAL) series hold the cooldown cadence — 84 with these
 # defaults. Beyond that the cadence stretches uniformly rather than breaking;
 # raise BATCH or lower INTERVAL. Keep BATCH x STAGGER under INTERVAL.