ci: use internal host IP 10.100.0.1 for SSH (hairpin NAT fix)

Runner is on the internal network — connecting to the public domain
fails due to hairpin NAT, same as the syndication webhook.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/deploy.yml

@@ -17,9 +17,9 @@ jobs:
           mkdir -p ~/.ssh
           printf '%s\n' "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/id_rsa
           chmod 600 ~/.ssh/id_rsa
-          ssh-keyscan -p ${{ secrets.SSH_PORT }} ${{ secrets.SSH_HOST }} >> ~/.ssh/known_hosts 2>/dev/null
+          ssh-keyscan -p ${{ secrets.SSH_PORT }} 10.100.0.1 >> ~/.ssh/known_hosts 2>/dev/null
 
-          ssh -p ${{ secrets.SSH_PORT }} ${{ secrets.SSH_USER }}@${{ secrets.SSH_HOST }} << SSHEOF
+          ssh -p ${{ secrets.SSH_PORT }} ${{ secrets.SSH_USER }}@10.100.0.1 << SSHEOF
           set -eu
           restart_log=/tmp/indiekit-restart.log