fix(icons): emit FA5 only and upgrade legacy FA4 icon values

The theme is FA5-only, but aksrt_icon_markup() prefixed bare glyphs with
the FA4 style token, so stored icon-picker values rendered FA4 markup,
and three runtime strings still carried the FA4 double-fa form (report
modal header and submit button, comment report menu item). That left the
navigation icon contract failing at 11/12.

- aksrt_icon_markup() normalizes bare glyphs, legacy FA4 values and
  style-only values to "fa fas fa-<glyph>", keeping the FA5 brand family
  (fa fab) and trailing classes intact.
- aksrt_normalize_icon_key() strips the legacy FA4 prefix so stored
  values resolve against the brand-icon catalog again.
- report.js and the comment report item emit FA5 markup.
- An icon-picker contract test locks the upgrade behaviour.

Verification: 338 widget-system, 12 navigation, 28 admin and 13
front-submit contract tests pass; normalization also exercised against
legacy, FA5 and brand inputs.

inc/helpers/comments/item.php

@@ -178,7 +178,7 @@ if (!function_exists('aksrt_get_comment_report_html')) :
 			'target_avatar' => get_avatar_url((int) $comment->user_id > 0 ? (int) $comment->user_id : 0, ['size' => 40]) ?: '',
 		]);
 
-		return '<li><a class="comment-report-link" href="javascript:;" data-aksrt-report="' . esc_attr((string) $report_payload) . '"><i class="fa fa-exclamation-triangle mr10 fa-fw c-red" aria-hidden="true"></i>' . esc_html__('举报', 'aksrt') . '</a></li>';
+		return '<li><a class="comment-report-link" href="javascript:;" data-aksrt-report="' . esc_attr((string) $report_payload) . '"><i class="fa fas fa-exclamation-triangle mr10 fa-fw c-red" aria-hidden="true"></i>' . esc_html__('举报', 'aksrt') . '</a></li>';
 	}
 endif;