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/components/Palette.tsx

@@ -28,7 +28,7 @@ function recent() {
 /** Move to the next/previous session relative to the open one. */
 function step(dir: 1 | -1) {
   const list = recent();
-  const cur = location.hash.match(/^#\/s\/([^/]+)/)?.[1];
+  const cur = location.hash.match(/^#\/s\/([^/+]+)/)?.[1];
   const i = list.findIndex((s) => s.id === cur);
   const next = list[i < 0 ? 0 : Math.min(Math.max(i + dir, 0), list.length - 1)];
   if (next) navigate(`/s/${next.id}`);