Make legal notice link configurable

The legal notice link in the navbar was hardcoded to the
bnvb website. Deployments without that legal notice showed
a dead link to a foreign site.

Move the URL into assets/config.json (legalNotice), like
the Nextcloud and adhoc buttons. The link stays hidden
unless the entry is configured.

assets/config.json.sample

@@ -2,6 +2,7 @@
   "jitsiLauncher": "server.domain.tld/subdir",
   "jitsiHost": "jit.si",
   "nextcloudBase": "https://cloud.domain.tld",
+  "legalNotice": "https://www.domain.tld/legal-notice",
   "allowAdhocMeetings": true,
   "launchTimeout": 2000,
   "backgroundImage": "path/to/backgroundimage",

assets/launch.js

@@ -382,6 +382,23 @@ function applyAdhocButton() {
   createAdhocButton.classList.remove("hidden");
 }
 
+/* ============================================================
+ * LEGAL NOTICE LINK
+ * ============================================================ */
+
+/*
+ * Only show if a legal notice URL is configured
+ * (CONFIG.legalNotice in assets/config.json).
+ */
+function applyLegalNoticeLink() {
+  if (!CONFIG.legalNotice || !legalNoticeLink) {
+    return;
+  }
+
+  legalNoticeLink.href = CONFIG.legalNotice;
+  legalNoticeLink.classList.remove("hidden");
+}
+
 /* ============================================================
  * DOM elements
  * ============================================================
@@ -432,6 +449,7 @@ const copyAdhocLinkButton = document.getElementById("copyAdhocLinkButton");
 const navbar = document.querySelector(".navbar");
 const navToggle = document.getElementById("navToggle");
 const navActions = document.getElementById("navActions");
+const legalNoticeLink = document.getElementById("legalNoticeLink");
 
 /* Language menu DOM elements */
 const langMenu = document.getElementById("langMenu");
@@ -1621,6 +1639,7 @@ async function start() {
   applyFavicons();
   applyNextcloudButton();
   applyAdhocButton();
+  applyLegalNoticeLink();
 
   await loadTranslations();