Persist terminal tabs and scrollback across restarts

[frenchie4111]

Summary

• Tab metadata (claude + shell only — diff tabs are transient) is now saved in config.json per worktree path and restored on app launch.
• xterm's SerializeAddon captures each terminal's buffer; history is written to userData/terminal-history/<id>.txt on a 30s interval and synchronously via beforeunload when the window closes.
• On mount, XTerminal loads any saved history, writes it to the fresh xterm with a ── session restored ── separator, then spawns a new pty — so users see their previous output scrolled above a fresh shell.
• Explicitly closing a tab or deleting a worktree marks the id as closing (suppressing pending saves) and deletes its history file. Orphaned history files are pruned on startup.

Caveats

• Scrollback is visual only. The shell process is new on each launch — env, cwd, and $? do not survive. Claude sessions still rely on claude --continue (already the default).
• xterm's default scrollback (1000 lines) caps per-terminal history file size.

Test plan

• Open a shell tab, type some commands, quit with Cmd-Q, reopen — tab reappears with scrollback visible above a fresh prompt.
• Same flow but close the tab explicitly before quitting — tab does not reappear and userData/terminal-history/ has no file for that id.
• Delete a worktree with active terminals — its history files are removed.
• Quit with multiple tabs across multiple worktrees — all restore correctly.

🤖 Generated with Claude Code