feat: add hashfs for static asset cache busting and live clock

- Add assets package with dev/prod build tags
- Dev: serve from filesystem with Cache-Control: no-store
- Prod: use hashfs for cache-busting URLs
- Add LiveClock component to show SSE connection status
- Update templates to use StaticPath for asset URLs

assets/assets.go

@@ -0,0 +1,5 @@
+// Package assets provides static file serving with build-tag switching
+// between live filesystem (dev) and embedded hashfs (prod).
+package assets
+
+const DirectoryPath = "assets"

assets/static_dev.go

@@ -0,0 +1,22 @@
+//go:build dev
+
+package assets
+
+import (
+	"net/http"
+	"os"
+
+	"github.com/rs/zerolog/log"
+)
+
+func Handler() http.Handler {
+	log.Debug().Str("path", DirectoryPath).Msg("static assets served from filesystem")
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Cache-Control", "no-store")
+		http.StripPrefix("/assets/", http.FileServerFS(os.DirFS(DirectoryPath))).ServeHTTP(w, r)
+	})
+}
+
+func StaticPath(path string) string {
+	return "/assets/" + path
+}

assets/static_prod.go

@@ -0,0 +1,26 @@
+//go:build !dev
+
+package assets
+
+import (
+	"embed"
+	"net/http"
+
+	"github.com/benbjohnson/hashfs"
+	"github.com/rs/zerolog/log"
+)
+
+var (
+	//go:embed css js
+	staticFiles embed.FS
+	staticSys   = hashfs.NewFS(staticFiles)
+)
+
+func Handler() http.Handler {
+	log.Debug().Msg("static assets are embedded with hashfs")
+	return hashfs.FileServer(staticSys)
+}
+
+func StaticPath(path string) string {
+	return "/" + staticSys.HashName(path)
+}