refactor(icons): replace local brand SVGs with FA5 classes

Unify social/OAuth/contact icons on the global Font Awesome 5.15.4 pack,
add aksrt_render_social_links for author hero, enqueue FA on admin SPA,
and delete assets/img/icons.

inc/classes/oauth-traits/trait-aksrt-oauth-part-2.php

@@ -16,14 +16,14 @@ trait AKSRT_OAuth_Part_2 {
             'baidu'  => 'Baidu',  'alipay' => 'Alipay',
         ];
         $icons = [
-            'github' => aksrt_inline_svg('github'),
-            'gitee'  => aksrt_inline_svg('gitee'),
-            'qq'     => aksrt_inline_svg('qq'),
-            'google' => aksrt_inline_svg('google'),
-            'weibo'  => aksrt_inline_svg('weibo'),
-            'weixin' => aksrt_inline_svg('wechat'),
-            'baidu'  => '<span class="oauth-btn__fallback">B</span>',
-            'alipay' => '<span class="oauth-btn__fallback">A</span>',
+            'github' => aksrt_brand_icon('github'),
+            'gitee'  => aksrt_brand_icon('gitee'),
+            'qq'     => aksrt_brand_icon('qq'),
+            'google' => aksrt_brand_icon('google'),
+            'weibo'  => aksrt_brand_icon('weibo'),
+            'weixin' => aksrt_brand_icon('weixin'),
+            'baidu'  => aksrt_brand_icon('baidu'),
+            'alipay' => aksrt_brand_icon('alipay'),
         ];
 
         $bindings = [];