integrate: FG Scan documentation into help system

- Add fg_scan.md to documentation routes mapping
- Add FG Scan link to help viewer navigation menu
- Add floating help button to fg_scan.html page
- Documentation now accessible from both:
  * Floating help button (📖) on fg_scan page
  * Help navigation menu in documentation viewer

py_app/app/routes.py

@@ -4229,6 +4229,7 @@ def help(page='dashboard'):
     # Map page names to markdown files
     doc_files = {
         'dashboard': 'dashboard.md',
+        'fg_scan': 'fg_scan.md',
         'print_module': 'print_module.md',
         'print_lost_labels': 'print_lost_labels.md',
         'daily_mirror': 'daily_mirror.md',