Add GUIDE section for v3 docs

docs/.vitepress/extensions.data.js

@@ -0,0 +1,40 @@
+import { readFileSync, existsSync } from 'node:fs'
+import { resolve, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const __dirname = dirname(fileURLToPath(import.meta.url))
+const DATA_PATH = resolve(__dirname, 'ext-data.json')
+const NOTES_PATH = resolve(__dirname, '../en/guide/extension-notes.md')
+
+export default {
+  watch: [DATA_PATH, NOTES_PATH],
+
+  load() {
+    if (!existsSync(DATA_PATH)) {
+      console.warn(
+        '[extensions.data.js] ext-data.json not found. ' +
+        'Run `bin/spc dev:gen-ext-docs` to generate it.'
+      )
+      return { extensions: [], missing: true }
+    }
+
+    const raw = JSON.parse(readFileSync(DATA_PATH, 'utf-8'))
+
+    // Build the set of extension names that have a section in extension-notes.md.
+    // Headings at level 2 or 3 are matched; leading/trailing whitespace is stripped.
+    const notesSet = new Set()
+    if (existsSync(NOTES_PATH)) {
+      const notesContent = readFileSync(NOTES_PATH, 'utf-8')
+      for (const match of notesContent.matchAll(/^#{2,3}\s+(\S+)/gm)) {
+        notesSet.add(match[1].toLowerCase())
+      }
+    }
+
+    const extensions = raw.extensions.map(ext => ({
+      ...ext,
+      hasNotes: notesSet.has(ext.name.toLowerCase()),
+    }))
+
+    return { extensions, missing: false }
+  },
+}