build(ci,deploy)!: the runner at home in a nightly window, deploys by hand (ADR 0039, D6, D13, D16)

The CI runner moves to halkyon.li's host at home and runs from 02:00 to
05:00 alone: a timer starts it, its unit's RuntimeMaxSec ends it, and
night.sh rests the instance's heavy sidecars around it as deploy, while
Caddy, PostgreSQL and the apps' servers keep serving. Jobs pushed during the
day wait in Forgejo's queue.

Its sandbox fits the new host: its folder on the HDD, the rest of /data
hidden, containerd's store out of reach, no private IPv4 network and no
IPv6 at all (the home network's IPv6 addresses are public ones under a
changing prefix, on the internet's own interface), 5 GB of memory with swap
beyond. The Sandbox step checks the tunnel, the home router and IPv6.

BREAKING CHANGE: CI deploys nothing any more: the deploy job goes with
learn.halkyon.eu's server, and halkyon.li deploys by hand with redeploy.sh
once a commit's night's run passed. Jobs run on the runner labelled
balthasar; sahaquiel's runner picks up none.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

deploy/runner/halkyon-night.timer

@@ -0,0 +1,12 @@
+# halkyon-night.service at 01:55:00 daily (ADR 0039, D6). As
+# /etc/systemd/system/halkyon-night.timer, enabled with
+# `systemctl enable --now halkyon-night.timer`.
+[Unit]
+Description=halkyon.li: night.sh stop at 01:55:00
+
+[Timer]
+OnCalendar=*-*-* 01:55:00
+Persistent=false
+
+[Install]
+WantedBy=timers.target