Document ntfy topic setup and why local should use a different one

Cooldown state is in memory, so every restart begins with an empty fired-zone
table and the first closed bar re-alerts whatever zone price is sitting on.
Locally, with --reload, that is every file save — which would push a stream of
duplicates to a phone sharing the production topic.

Also records that a production deploy resets cooldowns for the same reason, and
that ntfy topics are public in both directions.

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

README.md

@@ -150,6 +150,28 @@ To clear it: `localStorage.removeItem('chart-token')`.
 polls the latter from whatever machine you pushed from, and neither reveals
 anything about the market data or the configuration.
 
+## Alerts and ntfy
+
+Alerts are evaluated **server-side**, once per closed 1m bar, by a single engine
+living in `Runtime`. They do not depend on a browser being connected — that is the
+whole point of the phone push — and opening two tabs does not double-notify.
+
+`NTFY_TOPIC` must be set or nothing sends; `send_ntfy` returns immediately on a blank
+topic. Set it in **Coolify's environment variables** for production, not in this repo.
+
+**Use a different topic locally — or better, none.** Cooldown state is in memory, so
+every restart starts with empty cooldowns and the first closed bar re-alerts whatever
+zone price is sitting on. Locally that means every `--reload` save. Leaving
+`NTFY_TOPIC` blank keeps the in-browser sound and banner while suppressing the push;
+set a `-dev` topic only while testing the push path itself.
+
+The same applies to production, more slowly: **a deploy resets the cooldowns**, so a
+zone that alerted an hour ago can alert again right after a redeploy. Persisting the
+fired-zone table would fix it.
+
+Note that ntfy topics are public by default: anyone who knows the name can both read
+your alerts and publish to it. Treat the topic name as a secret.
+
 ## Saved trendlines
 
 Manual trendlines are written to `MANUAL_LINES_PATH` (`./data/manual_lines.json`).