[Feature]: add shortcut to reopen recently closed sessions

[velga111]

Problem statement

When users close a session by mistake, or need to jump back to a session they just closed while comparing multiple sessions, the current recovery path is too slow. They need to manually search or browse history to find the recently closed session again.

Proposed solution

Add a keyboard shortcut to reopen the most recently closed session.

Key behaviors:

• Reopen the most recently closed session when the shortcut is triggered.
• If the shortcut is triggered repeatedly, continue reopening sessions in reverse close order.
• If there are no recently closed sessions to restore, do nothing or show a lightweight hint.
• Use a default shortcut that does not conflict with existing TouchAI shortcuts or common OS/browser shortcuts.
• Expose the shortcut in keyboard shortcut settings so users can customize or disable it.

Alternatives considered

• Rely on the current history/search flow: works, but is slower for accidental closes and repeated session switching.
• Add only a UI button/menu item: useful as a secondary entry point, but less efficient than a keyboard shortcut for this workflow.

Main area

frontend (shortcut handling + session navigation), possibly tauri if the shortcut needs to work globally.

Risk boundaries

• AgentService or conversation runtime
• tool execution or instruction loading
• session navigation / restoration behavior
• MCP integration
• database schema or migrations

Mockups, screenshots, or examples

Reference behavior: browser-style reopen closed tab/session, such as Ctrl+Shift+T / Cmd+Shift+T. The exact default binding should follow TouchAI's existing shortcut system.

[ARCJ137442]

It's similar to the design and function of the command claude -c in Claude Code that can quick resume the last session.