rename admin-submit-wrap → admin-form-footer across all templates and CSS

- Updated 6 admin templates: add.php, edit.php, login.php, account.php,
  import.php, pages-edit.php — replaced <div class="admin-submit-wrap">
  with <div class="admin-form-footer">
- Updated 8 CSS selectors in admin.css:
  - .admin-form-footer { margin-top/padding-top } (was .admin-submit-wrap)
  - .admin-form > div:not(.admin-form-footer) grid exclusion guard (×3)
  - .admin-login-box .admin-form > div:not(.admin-form-footer) overrides (×2)
  - .admin-login-box .admin-form-footer compact spacing override
- No visual change; purely a semantic rename to a descriptive class name
- Also marked status-badge.php partial and WCAG 1.3.1 badge tasks as
  already-done in todo/02-php-components.md and todo/04-accessibility.md
  (partial + CSS were fully implemented but todo had not been updated)

public/admin/edit.php

@@ -176,7 +176,7 @@ try {
             </label>
         </div>
 
-        <div class="admin-submit-wrap">
+        <div class="admin-form-footer">
             <button type="submit" class="admin-btn">Enregistrer</button>
             <a href="/admin/thanks.php?id=<?= $thesisId ?>" class="admin-btn-secondary admin-cancel-link">Annuler</a>
         </div>