feat: Add SSH-Key support for secure deployment authentication

- upload.sh: Conditional SSH-Key vs. password authentication
- Automatic detection of SSH-Keys via FTP_SSH_KEY variable
- CloudPanel-compatible SSH-Key integration
- .env.upload.example: Added SSH-Key documentation
- Secure SFTP uploads without passwords in code

deployment/scripts/.env.upload.example

@@ -16,6 +16,10 @@ FTP_PATH="/htdocs"
 # SSH/SFTP Port (Standard: 22)
 FTP_PORT="22"
 
+# SSH-Key Authentifizierung (Optional, für SSH-Key-only Server)
+# Falls gesetzt, wird SSH-Key statt Passwort verwendet
+# FTP_SSH_KEY="$HOME/.ssh/id_rsa"
+
 # Beispiele für verschiedene Provider:
 # Strato:     FTP_HOST="ftp.strato.de"     FTP_PATH="/htdocs"
 # 1&1:        FTP_HOST="ftp.1und1.de"      FTP_PATH="/htdocs"