refactor(autoload): migrate theme classes to Composer PSR-4

Move 288 types from global AKSRT_* + inc/classes manual requires into
namespace AKSRT\{Domain} under src/AKSRT/, wire composer.json psr-4,
and slim bootstrap to helpers/modules/hooks only. Split multi-class
widget/gateway files, update admin contract audit paths, and document
the layout in ADR/README.

composer.json

@@ -1,6 +1,6 @@
 {
     "name": "aksrt/theme",
-    "description": "AKSRT WordPress Theme - OAuth dependencies",
+    "description": "AKSRT WordPress Theme",
     "type": "wordpress-theme",
     "require": {
         "php": ">=7.4",
@@ -14,5 +14,10 @@
         "audit": {
             "block-insecure": false
         }
+    },
+    "autoload": {
+        "psr-4": {
+            "AKSRT\\": "src/AKSRT/"
+        }
     }
-}
+}