fix: resolve partage form submission issues

- Replace mb_strlen/mb_substr/mb_strtolower with strlen/substr/strtolower
  (mbstring extension missing on server, causing fatal error)
- Scope annexes checkbox HTMX swap to #annexes-input-block with hx-select
  (prevents duplicating entire page inside Fichiers fieldset)
- Split format+fichiers response: #format-fichiers-block (stable) and
  #format-extras-block (swappable, inside Fichiers fieldset). Format
  checkboxes use hx-select to extract only the extras, preserving file queue.
- Keep format extras inline in Fichiers fieldset (no sub-fieldsets). Remove
  website legend input (URL only).
- When PeerTube upload disabled, show direct file upload inputs for
  video/audio (name=files[]).
- Add "Glissez-déposez" sort hint below TFE file queue.
- Fix .fq-name overflow with width:0;min-width:100% chain.
- Remove legend placeholder from .fq-item.
- Merge "Récits et expérimentation" AP into "Narration Spéculative".
  Rename PACS to "Pratique de lart - outils critiques, arts et contexte
  simultanés".
- Remove président·e field from jury fieldset, form templates, and
  controller validation. Keep DB column and display logic for existing data.

app/src/Database.php

@@ -1016,7 +1016,7 @@ class Database
         }
 
         $normalise = static function (string $s): string {
-            return preg_replace('/[^a-z0-9]/u', '', mb_strtolower($s));
+            return preg_replace('/[^a-z0-9]/u', '', strtolower($s));
         };
 
         $normNew = $normalise($title);
@@ -1036,11 +1036,11 @@ class Database
             }
 
             // Prefix match: one starts with the other (handles subtitle variations).
-            $maxLen = max(mb_strlen($normNew), mb_strlen($normExisting));
+            $maxLen = max(strlen($normNew), strlen($normExisting));
             if ($maxLen === 0) {
                 continue;
             }
-            $minLen = min(mb_strlen($normNew), mb_strlen($normExisting));
+            $minLen = min(strlen($normNew), strlen($normExisting));
             if ($minLen >= 5) { // avoid matching very short fragments
                 if (str_starts_with($normExisting, $normNew) || str_starts_with($normNew, $normExisting)) {
                     return [
@@ -1055,8 +1055,8 @@ class Database
 
             // Levenshtein distance ≤ 10 % of the longer string.
             // levenshtein() is limited to 255 chars; use substrings for safety.
-            $a = mb_substr($normNew, 0, 255);
-            $b = mb_substr($normExisting, 0, 255);
+            $a = substr($normNew, 0, 255);
+            $b = substr($normExisting, 0, 255);
             $dist      = levenshtein($a, $b);
             $threshold = (int)ceil($maxLen * 0.10);
             if ($dist <= $threshold) {