fix(ci): Use bracketed host:port format for demo host key

SSH looks up known_hosts entries for non-standard ports as
'[host]:port'. The demo entry lacked the brackets, so it only matched
port 22 and the deploy on port 820 failed host key verification. The
production entry already used the correct format.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: enko

.github/workflows/release.yml

@@ -328,7 +328,7 @@ jobs:
         run: |
           mkdir -p ~/.ssh
           echo "[node4.datenknoten.me]:820 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILOtQWdKnvQYP0gA5tnyYrTt+uGJDek3YGWSHi2M6f35" >> ~/.ssh/known_hosts
-          echo "demo.freundebuch.datenknoten.me ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBHs9Iw7r9+n+AtdAETA+Qw4fZkhuInOxxft+1Yc42tYhXY+XWyPGEuvTvikmWLglTNFlicv4uMdZ2i9FYamMlss=" >> ~/.ssh/known_hosts
+          echo "[demo.freundebuch.datenknoten.me]:820 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBHs9Iw7r9+n+AtdAETA+Qw4fZkhuInOxxft+1Yc42tYhXY+XWyPGEuvTvikmWLglTNFlicv4uMdZ2i9FYamMlss=" >> ~/.ssh/known_hosts
 
       - name: Deploy Production System
         env: