fix(tui): ensure cursor moves to end of content on exit to prevent overwriting/artifacts

[tallshort]

before: ctrl+c twice to exit, the last context usage status line got overwritten.

 1+1=?


 Thinking...

 1 + 1 = 2

───────────────────────────────────────────────────────────────────────────────

───────────────────────────────────────────────────────────────────────────────
~/workspace/pi-mono (main)

after fix: ctrl+c twice to exit, the status line is kept.

1+1=?


 Thinking...

 1 + 1 = 2

────────────────────────────────────────────────────────────────────────────────

────────────────────────────────────────────────────────────────────────────────
~/workspace/pi-mono (fix/cursor-on-exit)
↑695 ↓40 0.6%/128k                                        minimaxai/minimax-m2.1

[badlogic]

Merged to main with changelog entry. Thanks @tallshort!