feat(web): add automated build version tracking and update notification banner

cmd/server/main.go

@@ -47,9 +47,8 @@ import (
 // @host localhost:8080
 // @BasePath /api/v1
 // @schemes http https
-// @securityDefinitions.apikey SessionAuth
-// @in cookie
-// @name dumpster_session
+var GitSHA = "dev"
+
 func main() {
 	logger := slog.New(slog.NewTextHandler(os.Stdout, nil))
 
@@ -153,6 +152,14 @@ func main() {
 
 	// API routes
 	r.Route("/api/v1", func(r chi.Router) {
+		r.Get("/version", func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
+			json.NewEncoder(w).Encode(map[string]string{
+				"version": GitSHA,
+			})
+		})
+
 		// Auth (public: register, login, logout) with strict rate limiting
 		r.Route("/auth", func(r chi.Router) {
 			r.Use(middleware.RateLimit(5, 10)) // 5 req/s, burst 10