feat: add JSON Viewer support and related configurations (#643)

* feat: add JSON Viewer support and related configurations

* feat: add JSON Viewer initialization and theme switching support

apps/test/content/posts/json-viewer-test.md

@@ -0,0 +1,84 @@
+---
+title: JSON Viewer Test
+date: 2025-10-14T12:29:06+08:00
+collections:
+  - Tests
+categories:
+  - Markdown
+tags:
+  - json
+---
+
+Testing JSON viewer in FixIt theme.
+
+```json {boxed=false}
+{
+  "foo": "bar"
+}
+```
+
+<!--more-->
+
+## JSON Viewer
+
+```json
+{
+  "name": "John Doe",
+  "age": 30,
+  "isEmployed": true,
+  "address": {
+    "street": "123 Main St",
+    "city": "Anytown",
+    "state": "CA",
+    "postalCode": "12345"
+  },
+  "phoneNumbers": [
+    {
+      "type": "home",
+      "number": "555-1234"
+    },
+    {
+      "type": "work",
+      "number": "555-5678"
+    }
+  ],
+  "children": [],
+  "spouse": null
+}
+```
+
+disabled copy:
+
+```json {copyable=false}
+{
+  "foo": "bar"
+}
+```
+
+## JSON Code
+
+```json {enable=false}
+{
+  "name": "John Doe",
+  "age": 30,
+  "isEmployed": true,
+  "address": {
+    "street": "123 Main St",
+    "city": "Anytown",
+    "state": "CA",
+    "postalCode": "12345"
+  },
+  "phoneNumbers": [
+    {
+      "type": "home",
+      "number": "555-1234"
+    },
+    {
+      "type": "work",
+      "number": "555-5678"
+    }
+  ],
+  "children": [],
+  "spouse": null
+}
+```