feat: miller column browser, offline cache, search, breadcrumbs

- Dynamic miller column sizing with flexbox layout
- Root column (160px), middle slices (48px), active column (flex)
- Auto-scroll browser to rightmost column on navigation
- Offline indicator UI and IndexedDB cache integration
- /api/documents endpoint for client-side document caching
- Breadcrumb navigation in document content area
- FTS5 search with SQLite virtual table
- Client-side Mermaid and KaTeX rendering via CDN
- Deep sample content (advanced-topics/raft-deep-dive)
- Border removal (only search button keeps radius)
- Full viewport layout with proper borders between sidebar/content

apps/server/internal/httpserver/server.go

@@ -46,6 +46,9 @@ func New(deps Dependencies) (http.Handler, error) {
 		"trimMd": func(path string) string {
 			return strings.TrimSuffix(path, ".md")
 		},
+		"sub": func(a, b int) int {
+			return a - b
+		},
 	}).ParseFS(assets, "templates/*.gohtml")
 	if err != nil {
 		return nil, err
@@ -83,6 +86,8 @@ func New(deps Dependencies) (http.Handler, error) {
 	router.Post("/api/admin/workspace/sync", server.handleAdminWorkspaceSync)
 	router.Get("/docs", server.handleDocsIndex)
 	router.Get("/docs/*", server.handleDocument)
+	router.Get("/api/documents", server.handleDocuments)
+	router.Get("/api/search", server.handleSearch)
 	router.Post("/api/uploads", server.handleUpload)
 	router.Get("/attachments/{hash}", server.handleAttachment)
 	router.Handle("/static/*", http.StripPrefix("/static/", http.FileServer(mustSub("static"))))