Refactor runner and installation scripts for improved functionality

- Removed the `--disable-hiprt` flag from the runner command, simplifying the rendering options for users.
- Updated the `jiggablend-runner` script and README to reflect the removal of the HIPRT control flag, enhancing clarity in usage instructions.
- Enhanced the installation script to provide clearer examples for running the jiggablend manager and runner, improving user experience during setup.
- Implemented a more robust GPU backend detection mechanism, allowing for better compatibility with various hardware configurations.

internal/auth/auth.go

@@ -668,24 +668,42 @@ func (a *Auth) IsProductionModeFromConfig() bool {
 	return a.cfg.IsProductionMode()
 }
 
+func (a *Auth) writeUnauthorized(w http.ResponseWriter, r *http.Request) {
+	// Keep API behavior unchanged for programmatic clients.
+	if strings.HasPrefix(r.URL.Path, "/api/") {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusUnauthorized)
+		_ = json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
+		return
+	}
+
+	// For HTMX UI fragment requests, trigger a full-page redirect to login.
+	if strings.EqualFold(r.Header.Get("HX-Request"), "true") {
+		w.Header().Set("HX-Redirect", "/login")
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusUnauthorized)
+		_ = json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
+		return
+	}
+
+	// For normal browser page requests, redirect to login page.
+	http.Redirect(w, r, "/login", http.StatusFound)
+}
+
 // Middleware creates an authentication middleware
 func (a *Auth) Middleware(next http.HandlerFunc) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		cookie, err := r.Cookie("session_id")
 		if err != nil {
 			log.Printf("Authentication failed: missing session cookie for %s %s", r.Method, r.URL.Path)
-			w.Header().Set("Content-Type", "application/json")
-			w.WriteHeader(http.StatusUnauthorized)
-			json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
+			a.writeUnauthorized(w, r)
 			return
 		}
 
 		session, ok := a.GetSession(cookie.Value)
 		if !ok {
 			log.Printf("Authentication failed: invalid session cookie for %s %s", r.Method, r.URL.Path)
-			w.Header().Set("Content-Type", "application/json")
-			w.WriteHeader(http.StatusUnauthorized)
-			json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
+			a.writeUnauthorized(w, r)
 			return
 		}
 
@@ -717,18 +735,14 @@ func (a *Auth) AdminMiddleware(next http.HandlerFunc) http.HandlerFunc {
 		cookie, err := r.Cookie("session_id")
 		if err != nil {
 			log.Printf("Admin authentication failed: missing session cookie for %s %s", r.Method, r.URL.Path)
-			w.Header().Set("Content-Type", "application/json")
-			w.WriteHeader(http.StatusUnauthorized)
-			json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
+			a.writeUnauthorized(w, r)
 			return
 		}
 
 		session, ok := a.GetSession(cookie.Value)
 		if !ok {
 			log.Printf("Admin authentication failed: invalid session cookie for %s %s", r.Method, r.URL.Path)
-			w.Header().Set("Content-Type", "application/json")
-			w.WriteHeader(http.StatusUnauthorized)
-			json.NewEncoder(w).Encode(map[string]string{"error": "Unauthorized"})
+			a.writeUnauthorized(w, r)
 			return
 		}