feat(icons): load Bootstrap Icons and Font Awesome from the shared platform-tools packs

Register the icons packs in platform_connect, add fit_icon_assets() with local
fallback, and add a sysadmin 'Pacotes de icones' link to platform?tool=icons.

includes/auth_header.php

@@ -30,7 +30,7 @@ $app_name   = defined('APP_NAME') ? APP_NAME : 'FitMe 3070';
     </script>
     <link href="<?= base_url('assets/vendor/bootstrap5/css/bootstrap.min.css') ?>" rel="stylesheet">
     <link href="<?= htmlspecialchars(_asset_versioned('assets/css/bs-brand.css'), ENT_QUOTES) ?>" rel="stylesheet">
-    <link href="<?= base_url('assets/vendor/bootstrap-icons/bootstrap-icons.css') ?>" rel="stylesheet">
+    <?= fit_icon_assets(['bootstrap-icons'], ['assets/vendor/bootstrap-icons/bootstrap-icons.css']) ?>
     <style>
         :root {
           --bo-accent: #C2D500;