Split view, personal modes, budget warnings, server move script

- Up to three chats side by side (#/s/a+b+c), "Open beside" in the sidebar menu
- File manager tabs of a chat stored per user on the server (/sessions/{id}/tabs)
- Personal modes for every user (Settings → My modes, /account/modes)
- Budget meters (total, provider, images, opencode Go windows) with push warnings
  for admins at the warning share and 100 %, shown in the status overlay
- scripts/move-server.sh: move to another Docker host with bind mounts (Unraid);
  scripts/smoke-test.sh

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/whatsnew.ts

@@ -3,6 +3,20 @@
  * under "unreleased"; scripts/release.sh renames the key to the release version.
  */
 export const WHATS_NEW: Record<string, { en: string[]; de: string[] }> = {
+  unreleased: {
+    en: [
+      "Chats side by side: “Open beside” in a chat's menu in the sidebar",
+      "Settings → My modes: your own modes",
+      "Budget warnings as push notifications, budgets in the status overlay",
+      "File manager tabs are the same on every device",
+    ],
+    de: [
+      "Chats nebeneinander: „Daneben öffnen“ im Menü eines Chats in der Seitenleiste",
+      "Einstellungen → Meine Modi: eigene Modi",
+      "Budget-Warnungen als Push, Budgets im Status-Overlay",
+      "Dateimanager-Tabs sind auf jedem Gerät gleich",
+    ],
+  },
   "202611-00003": {
     en: [
       "Terminals and file managers as tabs in a chat – terminals keep running, also for another device",