WCAG 3.3.1: autofocus first invalid field on add/edit form validation failure

Add App::flashAutofocus(fieldName) and consumeAutofocus() to the thin App
helper so action handlers can identify which field caused a validation error
and the form page can move browser focus directly to it on reload.

Changes:
- src/App.php — flashAutofocus() stores field name in _flash_autofocus
  session key; consumeAutofocus() drains it and returns the name (or null)
- actions/formulaire.php — catch block maps exception messages to field
  names (auteurice, titre, synopsis, année, orientation, ap, finality,
  languages, tag, lien) and calls App::flashAutofocus()
- actions/edit.php — catch block maps common edit errors to field names
  and calls App::flashAutofocus()
- add.php — consumes the hint via App::consumeAutofocus() into
  $autofocusField; withAutofocus() helper merges autofocus=>true into
  $attrs for every field include; synopsis textarea gets inline autofocus
- edit.php — same pattern with inline ternary merges and textarea autofocus
- templates/partials/form/text-field.php — $attrs loop now emits bare
  attribute names (no ="...") when value === true, supporting autofocus,
  disabled, readonly etc. without special-casing
- templates/partials/form/select-field.php — same boolean-attr support
  added; $attrs variable initialised to [] when caller omits it

Closes WCAG 3.3.1 autofocus item in todo/04-accessibility.md.

public/admin/edit.php

@@ -53,6 +53,9 @@ try {
     // Set page title for header
     $pageTitle = "Éditer TFE - " . htmlspecialchars($thesis['title']);
 
+    // WCAG 3.3.1 — consume the autofocus hint stored by the edit action on validation failure.
+    $autofocusField = App::consumeAutofocus();
+
 } catch (Exception $e) {
     error_log("Error loading edit page: " . $e->getMessage());
     die("Erreur lors du chargement: " . $e->getMessage());
@@ -70,12 +73,13 @@ try {
         <input type="hidden" name="csrf_token" value="<?= htmlspecialchars($_SESSION['csrf_token']) ?>">
         <input type="hidden" name="thesis_id"  value="<?= $thesisId ?>">
 
-        <?php $name = 'auteurice'; $label = 'Auteur·ice(s) :'; $value = htmlspecialchars($thesis['authors']); $required = true; $attrs = ['autocomplete' => 'name'];  include APP_ROOT . '/templates/partials/form/text-field.php'; ?>
+        <?php $name = 'auteurice'; $label = 'Auteur·ice(s) :'; $value = htmlspecialchars($thesis['authors']); $required = true; $attrs = array_merge(['autocomplete' => 'name'], $autofocusField === 'auteurice' ? ['autofocus' => true] : []);  include APP_ROOT . '/templates/partials/form/text-field.php'; ?>
         <?php $name = 'mail';      $label = 'Contact :';        $value = '';                                   $attrs = ['autocomplete' => 'email']; include APP_ROOT . '/templates/partials/form/text-field.php'; ?>
 
         <?php
             $name  = 'année'; $label = 'Année :'; $value = htmlspecialchars((string)$thesis['year']); $required = true;
             $type  = 'number';
+            $attrs = $autofocusField === 'année' ? ['autofocus' => true] : [];
             include APP_ROOT . '/templates/partials/form/text-field.php';
         ?>
 
@@ -129,13 +133,14 @@ try {
 
         <?php $name = 'license_id'; $label = 'Licence :'; $options = $licenseTypes; $selected = $currentLicenseId; $placeholder = '- Inconnue -'; include APP_ROOT . '/templates/partials/form/select-field.php'; ?>
 
-        <?php $name = 'titre';    $label = 'Titre :';      $value = htmlspecialchars($thesis['title']);           $required = true; include APP_ROOT . '/templates/partials/form/text-field.php'; ?>
+        <?php $name = 'titre';    $label = 'Titre :';      $value = htmlspecialchars($thesis['title']);           $required = true; $attrs = $autofocusField === 'titre' ? ['autofocus' => true] : []; include APP_ROOT . '/templates/partials/form/text-field.php'; ?>
         <?php $name = 'subtitle'; $label = 'Sous-titre :'; $value = htmlspecialchars($thesis['subtitle'] ?? ''); include APP_ROOT . '/templates/partials/form/text-field.php'; ?>
 
         <!-- Synopsis (textarea — not covered by text-field partial) -->
         <div>
             <label for="synopsis">Synopsis :</label>
-            <textarea id="synopsis" name="synopsis" rows="7" required><?= htmlspecialchars($thesis['synopsis'] ?? '') ?></textarea>
+            <textarea id="synopsis" name="synopsis" rows="7" required
+                      <?= $autofocusField === 'synopsis' ? 'autofocus' : '' ?>><?= htmlspecialchars($thesis['synopsis'] ?? '') ?></textarea>
         </div>
 
         <?php $name = 'languages'; $label = 'Langue(s) :'; $options = $languages; $checked = $currentLanguages; include APP_ROOT . '/templates/partials/form/checkbox-list.php'; ?>