docs: add Lunr.js search with fuzzy matching and highlighting

Phase 4 part 1: Add search infrastructure
- Add SearchDoc struct and GenerateSearchIndex to docs handler
- Add stripHTML helper for plain text extraction
- Add ServeSearchIndex endpoint to http handler
- Add /docs/search-index.json route in main.go
- Search index includes all documentation files with ID, title, content, URL

internal/docs/handler.go

@@ -359,3 +359,59 @@ func (h *DocsHandler) GetAPIEndpointData(endpointPath string) (*templates.Endpoi
 
 	return nil, fmt.Errorf("endpoint not found: %s", endpointPath)
 }
+
+// SearchDoc represents a document for search indexing
+type SearchDoc struct {
+	ID      string `json:"id"`
+	Title   string `json:"title"`
+	Content string `json:"content"`
+	URL     string `json:"url"`
+}
+
+// GenerateSearchIndex generates a search index for all documentation
+func (h *DocsHandler) GenerateSearchIndex() ([]SearchDoc, error) {
+	docs, err := h.ListDocuments()
+	if err != nil {
+		return nil, fmt.Errorf("failed to list documents: %w", err)
+	}
+
+	var searchDocs []SearchDoc
+	for _, path := range docs {
+		doc, err := h.LoadDocument(path)
+		if err != nil {
+			continue
+		}
+
+		// Strip HTML tags for better search
+		content := h.stripHTML(doc.Content)
+
+		searchDocs = append(searchDocs, SearchDoc{
+			ID:      path,
+			Title:   doc.Title,
+			Content: content,
+			URL:     "/docs/" + strings.TrimSuffix(path, ".md"),
+		})
+	}
+
+	return searchDocs, nil
+}
+
+// stripHTML removes HTML tags from string
+func (h *DocsHandler) stripHTML(html string) string {
+	var result strings.Builder
+	inTag := false
+	for _, r := range html {
+		if r == '<' {
+			inTag = true
+			continue
+		}
+		if r == '>' {
+			inTag = false
+			continue
+		}
+		if !inTag {
+			result.WriteRune(r)
+		}
+	}
+	return result.String()
+}