fix: service restart on upgrade and no-cache headers for SPA assets

- postinst: restart instead of start if service already enabled (upgrade case)
- embed.go: no-cache/no-store on index.html, immutable cache on hashed assets
- Fixes web not refreshing after dpkg upgrade

internal/webui/embed.go

@@ -16,6 +16,7 @@ func ServeHTTP() http.Handler {
 }
 
 func ServeSPA() http.Handler {
+	fsHandler := http.FileServer(http.FS(distSub))
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		path := r.URL.Path
 		if path == "/favicon.ico" {
@@ -28,11 +29,15 @@ func ServeSPA() http.Handler {
 				http.Error(w, "not found", http.StatusNotFound)
 				return
 			}
-			w.Header().Set("Content-Type", "text/html")
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
+			w.Header().Set("Pragma", "no-cache")
+			w.Header().Set("Expires", "0")
 			w.Write(data)
 			return
 		}
-		http.FileServer(http.FS(distSub)).ServeHTTP(w, r)
+		w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
+		fsHandler.ServeHTTP(w, r)
 	})
 }