css: replace admin-form-row/admin-label/admin-input/select/textarea classes with semantic selectors

Remove five presentational classes from admin forms and replace with
structural CSS selectors scoped to .admin-form:

- .admin-form-row  → .admin-form > div:not(.admin-submit-wrap)
  Grid layout (260px label col + 1fr input col) applied directly to div
  children of the form; submit-wrap div excluded via :not().

- .admin-label     → .admin-form > div:not(.admin-submit-wrap) > label
  Scoped to the direct label child of each form row div; does not bleed
  into nested checkbox labels inside .admin-checkbox-list.

- .admin-input / .admin-select / .admin-textarea
  → .admin-form input:not([type=checkbox|radio|file|hidden|submit])
  → .admin-form select
  → .admin-form textarea
  Also extended to .admin-inline-form input/select (tags page) so the
  tags table inputs retain identical base styling and focus colour.

Templates updated: add.php, edit.php, login.php, account.php,
pages-edit.php, import.php, tags.php,
templates/partials/form/jury-fieldset.php — all class= attributes for
the five removed classes stripped.

import.php: added 'admin-form' class alongside 'admin-import-area' so
its single file-input row gets the grid row treatment; submit div was
already using admin-submit-wrap so it is correctly excluded.

No visual change — selectors target the same elements as before.

public/admin/import.php

@@ -338,11 +338,11 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_FILES['csv_file'])) {
     <p role="status" data-type="success">✓ <?= htmlspecialchars($message) ?></p>
     <?php endif; ?>
 
-    <form action="import.php" method="post" enctype="multipart/form-data" class="admin-import-area">
+    <form action="import.php" method="post" enctype="multipart/form-data" class="admin-import-area admin-form">
         <input type="hidden" name="csrf_token" value="<?= htmlspecialchars($_SESSION['csrf_token']) ?>">
 
-        <div class="admin-form-row" style="align-items:start;">
-            <label class="admin-label">Fichier CSV :</label>
+        <div>
+            <label>Fichier CSV :</label>
             <div class="admin-file-input">
                 <input type="file" id="csv_file" name="csv_file" accept=".csv" required>
                 <small style="margin-top:.5rem;">
@@ -352,7 +352,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_FILES['csv_file'])) {
             </div>
         </div>
 
-        <div style="margin-top:1rem;">
+        <div class="admin-submit-wrap">
             <button type="submit" class="admin-btn">Importer</button>
         </div>
     </form>