Lines 168-172 in show_template_preview() were missing >&2,
causing stdout leak into subshell capture chain.
This corrupted template_dir variable and broke Stealth mode deployment.
- All UI output (echo, printf) in interactive functions now goes to stderr (>&2)
- Only return values go to stdout for $() capture
- Affected: select_quick_domain, select_port, select_category, select_template, show_template_preview
- Also fixed: log_*, confirm, select_option in common.sh