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/config.yml

@@ -1,10 +1,11 @@
-# The Forgejo Actions runner of this repository's CI, on learn.halkyon.eu's server. Installed as
+# The Forgejo Actions runner of this repository's CI, on halkyon.li's host at home (ADR 0039,
+# D16), in the nightly window alone (forgejo-runner.timer). Installed as
 # /etc/forgejo-runner/config.yml, read by forgejo-runner.service (next to this file).
 # Written for forgejo-runner v13.1.0; its full reference: `forgejo-runner generate-config`.
 #
 # Jobs run directly on the host as the unprivileged user `runner`, never in containers:
-# running containers would take Docker access, which is root on the production server.
-# The systemd unit keeps the jobs away from production.
+# running containers would take Docker access, which is root on the instance's host.
+# The systemd unit keeps the jobs away from the instance and the home network.
 
 log:
   level: info
@@ -21,7 +22,7 @@ runner:
   fetch_interval: 10s
   report_interval: 1s
   # `runs-on: sahaquiel` in a workflow means: here, on the instance's server, on the host.
-  labels: ["sahaquiel:host"]
+  labels: ["balthasar:host"]
 
 cache:
   # No cache server (it would listen on a port of its own); the SDKs and package