feat: Skip archive creation if already up-to-date + better SSH key handling

Archive optimization:
- ✨ Checks if tar archive exists and is newer than all export files
- ⏭️ Skips archive creation if already up-to-date (saves time)
- 🔄 Recursively compares modification times in export directory
- 💪 Supports --force flag to override skip detection

SSH key improvements:
- ⚠️ Shows clear warning when SSH key is missing (instead of error)
- 📝 Informs user they'll be prompted for password
- 💡 Suggests adding SSH_PRIVATE_KEY to .env file
- 🔑 Allows deployment without SSH key (uses standard SSH auth)
- 🧹 Removed debug console.log statements

CLI changes:
- Changed SSH key check from hard error to warning
- Shows progress message about missing SSH key for 2 seconds
- Continues with deployment (user will enter password when prompted)