fix(ntfy): publish ntfy host port so the external reverse proxy can reach it

The ntfy service was configured with no published host port, on the
assumption that the public reverse proxy shares the compose network and
can dial ntfy:80 directly. It does not — Pangolin runs outside the
compose network and reaches every service through a published host port
(exactly why `app` publishes 3000). With no published port there was
nothing for the notification subdomain to forward to, so push delivery
could never work in production.

Publish container :80 on a host port (NTFY_HOST_PORT, default 2586,
binds 0.0.0.0 like `app`) and correct the now-inaccurate comments in
docker-compose.yml and ntfy/server.yml. Document NTFY_HOST_PORT in
.env.example. No code change — deploy config only.

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

.env.example

@@ -131,6 +131,12 @@ UOLINK_PROTOCOL=1
 #                         register endpoints on a different host than NTFY_BASE_URL.
 #   NTFY_PUBLISH_TOKEN    Optional. The content-free-tickle design needs NO token;
 #                         set one only to require auth on backend→ntfy publishes.
+#   NTFY_HOST_PORT        Host port the ntfy container publishes :80 on (default
+#                         2586). The public reverse proxy forwards the notification
+#                         subdomain to host:NTFY_HOST_PORT — required because the
+#                         proxy lives outside the compose network and cannot reach
+#                         ntfy any other way. Change only on a host-port conflict.
 NTFY_BASE_URL=https://ntfy.example.com
 # NTFY_ALLOWED_ORIGINS=https://ntfy.example.com
 # NTFY_PUBLISH_TOKEN=
+# NTFY_HOST_PORT=2586