Fix album scroll loading, lift 9-photo limit, badge import & mobile UX

Four user-reported fixes:

1. Albums infinite scroll: after a successful page load the
   IntersectionObserver wouldn't refire when the sentinel stayed in
   view (small thumbnails or large viewport), so subsequent pages
   needed a manual refresh. Re-check sentinel position after each
   load and add a scroll-event fallback for older mobile browsers.

2. 9-photo limit: add a "Больше 9 фото" toggle next to the photo
   source buttons. When checked, the cap lifts to 99 (covers Telegram
   auto-album splitting). VK still has its 9-attachment limit — if
   posting to VK with more selected, prompt a confirm and truncate
   the VK media payload to the first 9 client-side. Counters and
   notifications all read the dynamic max.

3. Badge tab: gallery selections now auto-import into the badge list
   on tab activation, so the photos appear right away with the first
   one opened in the editor. The "Выбранные в галерее Flickr" button
   reuses the same path for clarity.

4. Mobile UX: main navigation now scrolls horizontally on screens
   ≤720px instead of breaking into a tall stack — tabs stay on one
   row, scroll-snap on. In the badge editor the canvas wrapper is
   `position: sticky; top: 0` on screens ≤800px so the photo stays
   visible while scrolling through the controls below it; canvas
   also shrinks to ~62vw on phones.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

index.php

@@ -208,6 +208,10 @@ if (isset($_GET['logout'])) {
                             <span class="btn-icon-text">📤</span> Загрузить
                         </button>
                     </div>
+                    <label class="checkbox-label compact" style="margin-top:8px;">
+                        <input type="checkbox" id="chk-unlock-photo-limit">
+                        <span>Больше 9 фото (для Telegram). В VK уйдут только первые 9.</span>
+                    </label>
                     <div id="post-photos-preview" class="photos-preview combined-preview">
                         <p class="placeholder">Нажмите кнопку выше чтобы добавить фото</p>
                     </div>