Fix feedback spam: lock buttons after vote, add comment box on No

Voting now locks the widget for the page view (buttons disabled, chosen one highlighted, thank-you shown); reload to vote again. Fixes the CSS bug where display:flex overrode the hidden attribute so buttons stayed clickable. On No, an optional comment box posts to a separate Comment field. Adds a guarded [hidden] rule and selected/disabled/comment styles.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

en/student-welcome-guide/index.html

@@ -308,6 +308,12 @@
                     </div>
                     <p class="guide-feedback-msg guide-feedback-yes" hidden>Thanks, we are glad this helped.</p>
                     <p class="guide-feedback-msg guide-feedback-no" hidden>Thanks for telling us. Help us improve this page by writing what was missing to <a href="mailto:info@msosorg.com?subject=Guide%20feedback%3A%20From%20Macedonia%20to%20Slovenia%2C%20step%20by%20step">info@msosorg.com</a> or ask in our <a href="https://invite.viber.com/?g2=AQA8mf%2BZki%2FEk1GS2lyGTD6tc7SdqKmI5pVkOKT1jVasvZz0Lhn8esKYxjza9xoy" target="_blank" rel="noopener">Viber community</a>.</p>
+                    <div class="guide-feedback-comment" hidden>
+                        <label class="guide-feedback-comment-label" for="fbc-student-welcome-guide">What was missing or unclear? (optional)</label>
+                        <textarea id="fbc-student-welcome-guide" class="guide-feedback-comment-input" rows="3" placeholder="Tell us what we can improve on this page"></textarea>
+                        <button type="button" class="guide-feedback-comment-send">Send</button>
+                        <p class="guide-feedback-comment-thanks" hidden>Thanks, we received your note.</p>
+                    </div>
                 </div>
             </section>
         </section>