Make favicon paths configurable

The favicons were hardcoded in launch.html, so
rebranding the page required editing the template.

The paths now come from the favicons block in
assets/config.json. Missing keys keep the defaults
from launch.html.

assets/launch.js

@@ -309,6 +309,33 @@ function applyLogo() {
   logoBar.classList.remove("hidden");
 }
 
+/* ============================================================
+ * FAVICONS
+ * ============================================================
+ */
+
+/*
+ * Overwrite the default icons from launch.html
+ * (CONFIG.favicons in assets/config.json).
+ */
+function applyFavicons() {
+  if (!CONFIG.favicons) {
+    return;
+  }
+
+  if (CONFIG.favicons.ico) {
+    faviconIco.href = CONFIG.favicons.ico;
+  }
+
+  if (CONFIG.favicons.svg) {
+    faviconSvg.href = CONFIG.favicons.svg;
+  }
+
+  if (CONFIG.favicons.appleTouch) {
+    appleTouchIcon.href = CONFIG.favicons.appleTouch;
+  }
+}
+
 /* ============================================================
  * NEXTCLOUD BUTTON
  * ============================================================
@@ -412,6 +439,11 @@ const invalidRoomName = document.getElementById("invalidRoomName");
 const logoBar = document.getElementById("logoBar");
 const logoImage = document.getElementById("logoImage");
 
+/* Favicon DOM elements */
+const faviconIco = document.getElementById("faviconIco");
+const faviconSvg = document.getElementById("faviconSvg");
+const appleTouchIcon = document.getElementById("appleTouchIcon");
+
 /* Theme DOM elements */
 const themeButton = document.getElementById("themeButton");
 const themeIconSun = document.getElementById("themeIconSun");
@@ -1574,6 +1606,7 @@ async function start() {
 
   applyBackgroundImage();
   applyLogo();
+  applyFavicons();
   applyNextcloudButton();
   applyAdhocButton();