feat: add build-time doc index generator

Created scripts/generate-doc-index.js that:
- Scans all .md files under docs/
- Extracts titles, breadcrumbs, and URLs
- Strips Markdown syntax and tokenizes content with jieba
- Outputs structured index to static/doc-index.json

Also added static/doc-index.json to .gitignore

.gitignore

@@ -27,3 +27,7 @@ yarn-error.log*
 
 # Office temp files
 .~*
+.superpowers/
+
+# Generated search index
+static/doc-index.json

scripts/generate-doc-index.js

@@ -0,0 +1,107 @@
+const fs = require('fs');
+const path = require('path');
+
+// @node-rs/jieba is already a project dependency
+let jieba;
+try {
+  jieba = require('@node-rs/jieba');
+} catch {
+  console.warn('Warning: @node-rs/jieba not available, using simple character split');
+  jieba = { cut: (text) => [...new Set(text.replace(/[^一-龥a-zA-Z0-9]/g, ' ').split(/\s+/).filter(t => t.length > 1))] };
+}
+
+const DOCS_DIR = path.join(__dirname, '..', 'docs');
+const OUTPUT_PATH = path.join(__dirname, '..', 'static', 'doc-index.json');
+
+function stripMarkdown(md) {
+  return md
+    .replace(/^---[\s\S]*?---/m, '')       // frontmatter
+    .replace(/!\[.*?\]\(.*?\)/g, '')        // images
+    .replace(/\[([^\]]*)\]\(.*?\)/g, '$1')  // links → text
+    .replace(/#{1,6}\s/g, '')               // headings
+    .replace(/(\*{1,3}|_{1,3})(.*?)\1/g, '$2') // bold/italic
+    .replace(/`{1,3}[^`]*`{1,3}/g, '')     // inline code
+    .replace(/<[^>]+>/g, '')                // HTML tags
+    .replace(/\n{2,}/g, '\n')              // extra newlines
+    .trim();
+}
+
+function getBreadcrumb(docDir) {
+  const parts = [];
+  let current = docDir;
+
+  while (current !== DOCS_DIR) {
+    const categoryFile = path.join(current, '_category_.json');
+    if (fs.existsSync(categoryFile)) {
+      const cat = JSON.parse(fs.readFileSync(categoryFile, 'utf-8'));
+      parts.unshift(cat.label);
+    }
+    current = path.dirname(current);
+  }
+
+  return parts.join(' > ');
+}
+
+function getUrl(docPath) {
+  const relPath = path.relative(DOCS_DIR, docPath);
+  const withoutExt = relPath.replace(/\.md$/, '');
+  if (withoutExt === 'intro') return '/';
+  return '/' + withoutExt;
+}
+
+function getTitle(docPath, content) {
+  const fmMatch = content.match(/sidebar_label:\s*['"]?(.+?)['"]?\s*$/m);
+  if (fmMatch) return fmMatch[1].trim();
+  const headingMatch = content.match(/^#{1,6}\s+(.+)$/m);
+  if (headingMatch) return headingMatch[1].trim();
+  return path.basename(docPath, '.md');
+}
+
+function tokenize(text) {
+  const tokens = jieba.cut(text);
+  return [...new Set(tokens.filter(t => t.length > 1 && !/^[\s\d\W]+$/.test(t)))];
+}
+
+function processDoc(filePath) {
+  const content = fs.readFileSync(filePath, 'utf-8');
+  const text = stripMarkdown(content);
+  const title = getTitle(filePath, content);
+  const breadcrumb = getBreadcrumb(path.dirname(filePath));
+  const url = getUrl(filePath);
+  const tokens = tokenize(text);
+
+  const fullBreadcrumb = breadcrumb ? `${breadcrumb} > ${title}` : title;
+
+  return { title, text, tokens, breadcrumb: fullBreadcrumb, url };
+}
+
+function walkDocs(dir) {
+  const entries = fs.readdirSync(dir, { withFileTypes: true });
+  const mdFiles = [];
+
+  for (const entry of entries) {
+    const fullPath = path.join(dir, entry.name);
+    if (entry.name === 'superpowers') continue;
+    if (entry.isDirectory()) {
+      mdFiles.push(...walkDocs(fullPath));
+    } else if (entry.name.endsWith('.md')) {
+      mdFiles.push(fullPath);
+    }
+  }
+  return mdFiles;
+}
+
+function main() {
+  console.log('Generating document index...');
+  const mdFiles = walkDocs(DOCS_DIR);
+  console.log(`Found ${mdFiles.length} markdown files`);
+
+  const index = mdFiles.map(processDoc);
+  const totalTokens = index.reduce((sum, doc) => sum + doc.tokens.length, 0);
+  console.log(`Index: ${index.length} docs, ${totalTokens} total unique tokens`);
+
+  fs.writeFileSync(OUTPUT_PATH, JSON.stringify(index, null, 2), 'utf-8');
+  console.log(`Written to ${OUTPUT_PATH}`);
+}
+
+main();