ci(deploy): switch from rsync to lftp mirror (SFTP-only hosting)

Hetzner Webhosting accepts SSH for file transfer but refuses remote
command exec, failing rsync with:

  exec request failed on channel 0
  rsync error: error in rsync protocol data stream (code 12)

rsync over SSH requires spawning a remote rsync binary, which isn't
possible on SFTP-only tiers. Switch the mirror to lftp, which speaks
SFTP end-to-end. Same semantics (upload + delete removed files), same
key + known_hosts pinning via sftp:connect-program.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -96,27 +96,35 @@ jobs:
           chmod 600 ~/.ssh/id_ed25519
           printf '%s\n' "$SFTP_KNOWN_HOSTS" > ~/.ssh/known_hosts
           chmod 644 ~/.ssh/known_hosts
-          # Ensure rsync + openssh are present even on a minimal runner image.
-          if ! command -v rsync >/dev/null 2>&1 || ! command -v ssh >/dev/null 2>&1; then
+          # Hetzner Webhosting accounts are SFTP-only — they accept SSH for file
+          # transfer but refuse remote command exec ("exec request failed on
+          # channel 0"). rsync over SSH needs to spawn a remote rsync binary,
+          # so it cannot work here. Use lftp's mirror instead, which speaks
+          # SFTP end-to-end with the same key + known_hosts pinning.
+          if ! command -v lftp >/dev/null 2>&1 || ! command -v ssh >/dev/null 2>&1; then
             if command -v sudo >/dev/null 2>&1; then SUDO=sudo; else SUDO=; fi
             $SUDO apt-get update -qq
-            $SUDO apt-get install -y --no-install-recommends rsync openssh-client
+            $SUDO apt-get install -y --no-install-recommends lftp openssh-client
           fi
 
-      - name: Deploy via rsync
+      - name: Deploy via lftp (mirror over SFTP)
         env:
           SFTP_USER: ${{ secrets.SFTP_USER }}
           SFTP_HOST: ${{ secrets.SFTP_HOST }}
           SFTP_PATH: ${{ secrets.SFTP_PATH }}
         run: |
-          # Fail loudly if any secret is missing — otherwise rsync --delete
+          # Fail loudly if any secret is missing — otherwise mirror --delete
           # could be directed at the SSH user's home root.
           : "${SFTP_USER:?SFTP_USER secret must be set}"
           : "${SFTP_HOST:?SFTP_HOST secret must be set}"
           : "${SFTP_PATH:?SFTP_PATH secret must be set}"
-          rsync -avz --delete \
-            -e "ssh -i ~/.ssh/id_ed25519 -o StrictHostKeyChecking=yes -o UserKnownHostsFile=~/.ssh/known_hosts" \
-            dist/ "$SFTP_USER@$SFTP_HOST:$SFTP_PATH/"
+          lftp <<LFTP
+            set cmd:fail-exit yes
+            set sftp:connect-program 'ssh -a -x -i $HOME/.ssh/id_ed25519 -o StrictHostKeyChecking=yes -o UserKnownHostsFile=$HOME/.ssh/known_hosts'
+            open sftp://$SFTP_USER@$SFTP_HOST
+            mirror --reverse --delete --verbose --parallel=4 dist/ $SFTP_PATH/
+            bye
+          LFTP
 
       - name: Post-deploy smoke test
         run: |