tui: saved tabs are shared between local and remote servers

Description

The V2 TUI shares saved session tabs between the managed local server and explicit remote servers. Opening another server can restore the previous server's tabs, and changing that layout can affect the tabs restored when returning.

Each server should restore its own tabs in both global and current-directory scopes. Selected terminal panes should also stay separate, even when servers have identical session or terminal IDs.

Steps to reproduce

1. Open the managed local TUI and leave some session tabs open.
2. Exit, then launch with --server <remote-url> using the same TUI storage channel. For current-directory scope, use the same launch directory.
3. Observe that saved tabs are shared with the other server.
4. Change the remote layout, exit, and return locally. The local layout should remain independent.

Related references

• #37667: switching servers.
• #45346: opening remote sessions as tabs.
• #18302: an analogous persisted-state bug in the desktop app; this report concerns the TUI.