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/public/assets/css/admin.css

@@ -379,6 +379,11 @@ th.admin-ap-col {
 
 .admin-body table .thesis-title {
     font-weight: 500;
+    display: -webkit-box;
+    -webkit-line-clamp: 2;
+    -webkit-box-orient: vertical;
+    overflow: hidden;
+    word-break: break-word;
 }
 
 .admin-body table .thesis-subtitle {
@@ -1943,3 +1948,26 @@ th.admin-ap-col {
     margin: 0;
   }
 }
+
+/* ── Active search loading indicator ───────────────────────────────────── */
+.admin-search-indicator {
+  display: block;
+  height: 2px;
+  background: var(--accent-primary);
+  opacity: 0;
+  transition: opacity 0.15s;
+  pointer-events: none;
+  margin-top: var(--space-2xs);
+}
+
+.admin-search-indicator.htmx-request {
+  opacity: 1;
+  animation: admin-search-progress 1.2s ease-in-out infinite;
+}
+
+@keyframes admin-search-progress {
+  0%   { transform: scaleX(0);   transform-origin: left;  }
+  50%  { transform: scaleX(1);   transform-origin: left;  }
+  50.01% { transform: scaleX(1); transform-origin: right; }
+  100% { transform: scaleX(0);   transform-origin: right; }
+}