Scope localStorage keys per app directory

localStorage is scoped per origin, not per path. Multiple
jitsi-launch instances on one origin (e.g. meet.bnvb.eu/i
and /p) therefore shared one language and one theme
setting, and changing it in one instance changed it in
all others.

Prefix the language and theme keys with the app directory
derived from the page path. Each instance keeps its own
state; a root deployment gets the "/" prefix and behaves
as before. Previously saved choices reset once because
the key names change.

assets/launch.js

@@ -12,6 +12,20 @@
 let CONFIG = {};
 const CONFIG_URL = "assets/config.json";
 
+/*
+ * localStorage is scoped per origin, not per path.
+ * Prefix keys with the app directory so parallel
+ * instances (e.g. meet.bnvb.eu/i and /p) stay
+ * independent.
+ *
+ * "/p/launch.html" becomes "/p/"
+ */
+const STORAGE_PREFIX =
+  window.location.pathname.replace(/[^/]*$/, "");
+
+const LANGUAGE_KEY = STORAGE_PREFIX + "jitsiLauncherLanguage";
+const THEME_KEY = STORAGE_PREFIX + "jitsiLauncherTheme";
+
 /* ============================================================
  * Translations
  * ============================================================
@@ -34,7 +48,7 @@ function detectLanguage() {
    * Saved language choice takes precedence.
    */
   try {
-    const saved = localStorage.getItem("jitsiLauncherLanguage");
+    const saved = localStorage.getItem(LANGUAGE_KEY);
 
     if (saved && TRANSLATIONS[saved]) {
       return saved;
@@ -179,7 +193,7 @@ function setLanguage(language) {
   translation = TRANSLATIONS[language];
 
   try {
-    localStorage.setItem("jitsiLauncherLanguage", language);
+    localStorage.setItem(LANGUAGE_KEY, language);
   } catch (error) {
     /*
      * localStorage can be blocked, e.g. in private mode.
@@ -225,8 +239,6 @@ function closeNavMenu() {
  * ============================================================
  */
 
-const THEME_KEY = "jitsiLauncherTheme";
-
 function savedTheme() {
   try {
     const saved = localStorage.getItem(THEME_KEY);