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/Budget.tsx

@@ -44,7 +44,7 @@ interface BudgetData {
   providers: BudgetRow[];
 }
 
-function Bar({ share, warning, exceeded }: { share: number; warning: boolean; exceeded: boolean }) {
+export function Bar({ share, warning, exceeded }: { share: number; warning: boolean; exceeded: boolean }) {
   const color = exceeded ? "var(--red)" : warning ? "var(--accent2)" : "var(--green)";
   return (
     <div className="budget-bar" role="meter" aria-valuenow={Math.round(share * 100)} aria-valuemin={0} aria-valuemax={100}>