deploy: remove the CI pipeline; deploys are manual

No runner was ever active, so the pipeline never ran. Removes
.gitea/workflows/deploy.yml and the CI key and runner IP from
host/bootstrap.sh (a re-run removes the key an earlier bootstrap installed).
The README makes "Manual deploy" the one documented procedure: commit on main,
shellcheck in Docker (-S warning; the pipeline's lint step), git archive over
root SSH, deploy.sh as user deploy, the outside checks, then push.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/lib.sh

@@ -57,8 +57,8 @@ die() { log "ERROR: $*"; exit 1; }
 # is absolute, so nothing needs the caller's directory.
 cd /
 
-# acquire_lock <seconds>: deploy.sh and rollback.sh share this lock, so a CI
-# deploy and a manual rollback never run at the same time. Held until exit.
+# acquire_lock <seconds>: deploy.sh and rollback.sh share this lock, so a
+# deploy and a rollback never run at the same time. Held until exit.
 acquire_lock() {
   exec 9>>"$LOCK_FILE"
   flock -w "$1" 9 || die "another deploy or rollback holds $LOCK_FILE (waited $1 s)"