docs: add icon to API Reference navbar link and localize logo paths (#47)

Make the API Reference entry more discoverable in the navbar by adding
a code icon. Also switch logo references from the OSS CDN to local
/logo paths for self-contained assets.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ysyneu

docs.json

@@ -9,8 +9,8 @@
     "dark": "#8B5CF6"
   },
   "logo": {
-    "light": "https://flashduty-docs.oss-cn-beijing.aliyuncs.com/images/saas-logo.svg",
-    "dark": "https://flashduty-docs.oss-cn-beijing.aliyuncs.com/images/saas-logo-white.svg",
+    "light": "/logo/saas-logo.svg",
+    "dark": "/logo/saas-logo-white.svg",
     "href": "https://flashcat.cloud/"
   },
   "seo": {
@@ -1915,6 +1915,7 @@
     "links": [
       {
         "label": "API Reference",
+        "icon": "code",
         "href": "/zh/openapi/introduction"
       }
     ],