chore: the servers are named by the domain they serve

Files called the servers by their own host names, which are the
operator's and say nothing a reader needs. They now say which domain a
server serves: learn.halkyon.eu's server (the instance and its CI
runner), the halkyon.app server (Forgejo and the F-Droid repository).

Two names are settings rather than words. CI's runner label becomes
`instance` (`runs-on: instance`, `labels: ["instance:host"]`): the
runner reads its installed copy of deploy/runner/config.yml, so jobs
wait in the queue until that copy is updated and the runner restarted.
The SSH aliases the scripts and docs use become `learn-deploy` and
`fdroid-upload`. AGENTS.md says to keep it so.

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

@@ -1,4 +1,4 @@
-# The Forgejo Actions runner of this repository's CI, on sahaquiel. Installed as
+# The Forgejo Actions runner of this repository's CI, on learn.halkyon.eu's server. 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`.
 #
@@ -16,12 +16,12 @@ runner:
   timeout: 1h
   shutdown_timeout: 10m
   fetch_timeout: 30s
-  # How often to ask Forgejo for work. The default (2 s) is needless load on ramiel,
-  # a one-core server.
+  # How often to ask Forgejo for work. The default (2 s) is needless load on
+  # code.halkyon.app's server, a one-core one.
   fetch_interval: 10s
   report_interval: 1s
-  # `runs-on: sahaquiel` in a workflow means: here, on the host.
-  labels: ["sahaquiel:host"]
+  # `runs-on: instance` in a workflow means: here, on the instance's server, on the host.
+  labels: ["instance:host"]
 
 cache:
   # No cache server (it would listen on a port of its own); the SDKs and package