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/router.ts

@@ -15,3 +15,23 @@ export function useRoute(): string[] {
 export function navigate(path: string) {
   location.hash = path.startsWith("/") ? path : `/${path}`;
 }
+
+/** Chats shown side by side: #/s/<id>+<id>+<id> (at most 3). */
+export const MAX_PANES = 3;
+
+export function openChats(): string[] {
+  const m = location.hash.match(/^#\/s\/([^/]+)/);
+  return m ? m[1].split("+").filter(Boolean) : [];
+}
+
+/** Add a chat as another column (replaces the last one when all columns are used). */
+export function openBeside(id: string) {
+  const ids = openChats().filter((x) => x !== id);
+  if (ids.length >= MAX_PANES) ids.pop();
+  navigate(`/s/${[...ids, id].join("+")}`);
+}
+
+export function closePane(id: string) {
+  const ids = openChats().filter((x) => x !== id);
+  navigate(ids.length ? `/s/${ids.join("+")}` : "/");
+}