fix: Web GUI je vracao 404 iza nginx prefiksa

Flask slusa na rootu, a nginx ga proxira na ${GUI_PATH} (/guacadmin/).
Bez SCRIPT_NAME-a svi redirecti i url_for pozivi generirali su putanje
izvan prefiksa - / je redirectao na /login, sto nginx ne poznaje, pa je
GUI bio potpuno nedostupan (404 odmah nakon otvaranja).

Dodan PrefixMiddleware koji postavlja SCRIPT_NAME iz nove GUI_PATH
env varijable; systemd unit je sad prosljedjuje. Isto primijenjeno na
webgui/app.py i na inline kopiju u install.sh.

Provjereno: /guacadmin/ -> /guacadmin/login -> login -> /guacadmin/dashboard
(200), svi navigacijski linkovi ostaju pod prefiksom.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

install.sh

@@ -644,6 +644,28 @@ NGINX_CONFS  = ['/etc/nginx/sites-available/guacamole',
 app = Flask(__name__, template_folder='templates')
 app.secret_key = os.environ.get('SECRET_KEY', secrets.token_hex(32))
 
+
+class PrefixMiddleware:
+    """Nginx proxira GUI_PATH (npr. /guacadmin/) na Flask koji slusa na
+    rootu. Bez SCRIPT_NAME-a url_for i redirecti generiraju putanje izvan
+    prefiksa (/login umjesto /guacadmin/login) i nginx vraca 404."""
+
+    def __init__(self, wsgi_app, prefix=''):
+        self.wsgi_app = wsgi_app
+        prefix = (prefix or '').strip('/')
+        self.prefix = '/' + prefix if prefix else ''
+
+    def __call__(self, environ, start_response):
+        if self.prefix:
+            environ['SCRIPT_NAME'] = self.prefix
+            path = environ.get('PATH_INFO', '')
+            if path.startswith(self.prefix):
+                environ['PATH_INFO'] = path[len(self.prefix):] or '/'
+        return self.wsgi_app(environ, start_response)
+
+
+app.wsgi_app = PrefixMiddleware(app.wsgi_app, os.environ.get('GUI_PATH', ''))
+
 def load_config():
     if os.path.exists(CONFIG_FILE):
         with open(CONFIG_FILE) as f:
@@ -1713,6 +1735,7 @@ User=root
 WorkingDirectory=${WEBGUI_DIR}
 Environment=PORT=${GUI_PORT}
 Environment=SECRET_KEY=${GUI_SECRET}
+Environment=GUI_PATH=${GUI_PATH}
 ExecStart=${WEBGUI_DIR}/venv/bin/python3 ${WEBGUI_DIR}/app.py
 Restart=on-failure
 RestartSec=5