Add language-search component for Autre Langue input + active search in lists

Mirrors the mots-clé tag-search system: dropdown suggestions from
existing languages via HTMX, pill display with bin-icon remove buttons,
'Créer' option for new languages. Replaces the plain text input.

- New partial: templates/partials/form/language-search.php
- New fragment: public/partage/language-search-fragment.php
- Admin wrapper: public/admin/language-search-fragment.php
- Updated language-autre-fragment to return just the required asterisk indicator
- Updated both controllers to handle language_autre as array (pill-based)
  with backward-compatible string path
- Updated edit form to compute selectedOtherLanguages from DB
- Registered new route in partage/index.php
- Fix CSV importer: split comma-separated language column into individual entries
- Add htmx active search to admin index, title line-clamp, predefined languages only in checkboxes
- Admin index: filter form now uses htmx triggers (input delay:300ms on search,
  change on selects) to actively search without page reload
- Sort links include hx-push-url for back-button support
- Added loading indicator bar (.admin-search-indicator)
- Title column: line-clamp at 2 lines with overflow hidden, native title attr
  tooltip for full text
- Language checkboxes now show only 3 predefined languages (Français, Anglais,
  Néerlandais); all others go via the Autre langue search component
- Added Database::getPredefinedLanguages() and excluded predefined from
  language-search-fragment suggestions
- Included hidden sort/dir inputs in table-wrap so sort state preserved across
  filter changes
- Fix language-search: block 'Créer' for predefined languages in dropdown
  The 'Créer' option in the language-search dropdown now also checks against the
  predefined set (français, anglais, néerlandais) to avoid offering creation of
  languages that already exist as checkboxes.

app/templates/admin/index.php

@@ -43,7 +43,15 @@ document.addEventListener('htmx:afterSwap',()=>{document.querySelectorAll('input
             </div>
         </div>
 
-        <form class="admin-filters" method="get" action="/admin/">
+        <form id="admin-filter-form" class="admin-filters" method="get" action="/admin/"
+              hx-get="/admin/"
+              hx-trigger="change from:select, input changed delay:300ms from:input[name=search], keyup[key=='Enter'] from:input[name=search]"
+              hx-target="#admin-table-wrap"
+              hx-swap="innerHTML"
+              hx-indicator="#admin-search-indicator"
+              hx-include="#admin-filter-form, #admin-table-wrap input[name=sort], #admin-table-wrap input[name=dir]"
+              hx-push-url="true"
+              hx-sync="#admin-filter-form:replace">
             <input type="text" name="search" placeholder="Titre, auteur..."
                    value="<?= htmlspecialchars($searchQuery) ?>">
             <select name="year">
@@ -68,12 +76,13 @@ document.addEventListener('htmx:afterSwap',()=>{document.querySelectorAll('input
                     </option>
                 <?php endforeach; ?>
             </select>
-            <button type="submit" class="btn btn--primary btn--sm admin-filters-btn">Filtrer</button>
             <?php if ($searchQuery || $yearFilter || $orientationFilter || $apFilter): ?>
-                <button type="button" class="btn btn--secondary btn--sm admin-filters-reset"
-                        onclick="window.location='/admin/'">&#x2715; Réinitialiser</button>
+                <a href="/admin/" class="btn btn--secondary btn--sm admin-filters-reset">&#x2715; Réinitialiser</a>
             <?php endif; ?>
         </form>
+
+        <!-- Loading indicator bar -->
+        <div id="admin-search-indicator" class="admin-search-indicator"></div>
     </div>
 
     <?php include APP_ROOT . '/templates/admin/index-table.php'; ?>