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/templates/docs/help_viewer.html

@@ -169,6 +169,7 @@
         <div class="help-navigation">
             <strong>Documentație disponibilă:</strong>
             <a href="{{ url_for('main.help', page='dashboard') }}">Dashboard</a>
+            <a href="{{ url_for('main.help', page='fg_scan') }}">FG Scan - Scanare Produse</a>
             <a href="{{ url_for('main.help', page='etichete') }}">Modul Etichete</a>
             <a href="{{ url_for('main.help', page='print_module') }}">Print Module</a>
             <a href="{{ url_for('main.help', page='print_lost_labels') }}">Print Lost Labels</a>