docs: add source tag (#26884)

docs/3.api/2.composables/use-id.md

@@ -1,6 +1,11 @@
 ---
 title: "useId"
 description: Generate an SSR-friendly unique identifier that can be passed to accessibility attributes.
+links:
+  - label: Source
+    icon: i-simple-icons-github
+    to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/id.ts
+    size: xs
 ---
 
 ::important

docs/3.api/2.composables/use-preview-mode.md

@@ -1,6 +1,11 @@
 ---
 title: "usePreviewMode"
 description: "Use usePreviewMode to check and control preview mode in Nuxt"
+links:
+  - label: Source
+    icon: i-simple-icons-github
+    to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/preview.ts
+    size: xs
 ---
 
 # `usePreviewMode`