fix: disable mouse tracking on terminal exit (#838)

[MrRealORG]

Summary

Fixes #838: terminal mouse tracking not cleaned up on abnormal exit.

Problem

When MiMo Code is killed by an external process (e.g. another TUI tool), the terminal mouse event tracking escape sequences are not disabled. This leaves the terminal in mouse-tracking mode, causing garbage output like [555;row;colM on every mouse movement.

Root Cause

The exit handler in exit.tsx writes SGR reset + cursor show + OSC color resets, but does not send mouse tracking disable sequences. The renderer.destroy() should handle this during normal exit, but on abnormal exit (SIGTERM from external process), the renderer teardown may not complete.

Fix

Two-layer defense:

1. Async exit handler: Added mouse tracking disable sequences (modes 1000, 1002, 1003, 1005, 1006, 1015) to the ANSI cleanup string that runs during the normal exit flow.

2. Synchronous process.on("exit") hook: A safety net that runs even when the async exit handler cannot complete (e.g. SIGTERM from an external process). Node.js guarantees process.on("exit") callbacks run synchronously before the process exits, regardless of how the process was signaled.

Mouse modes disabled

Mode	Description
?1000	Basic tracking (X10 mouse)
?1002	Button-event tracking
?1003	Any-event tracking
?1005	UTF-8 extended coordinates
?1006	SGR extended coordinates
?1015	URXVT extended coordinates

Test Plan

• Launch MiMo Code, then kill -TERM <pid> from another terminal → verify no garbage on mouse move
• Normal exit (ESC ESC /quit) → verify terminal works normally
• Verify mouse still works during normal MiMo Code usage

Closes #838

[Ivaloz]

Summary

• Add mouse event tracking disable sequences (\e[?1000l, \e[?1002l, \e[?1003l, \e[?1006l) to the TUI exit handler's ANSI cleanup string
• Fixes terminal garbage output ([row;colM sequences) when MiMo Code is killed by an external process

Problem

When MiMo Code is killed by signal (e.g. another TUI tool like Qoder terminates it), the terminal's mouse event tracking is not properly disabled. This leaves the terminal in mouse-tracking mode, producing garbage escape sequences on every mouse move.

Root Cause

packages/opencode/src/cli/cmd/tui/context/exit.tsx wrote SGR reset + cursor show + OSC color resets on exit, but did not send mouse tracking disable sequences. On abnormal exit, renderer.destroy() may not complete its teardown.

Fix

Prepend \x1b[?1000l\x1b[?1002l\x1b[?1003l\x1b[?1006l to the exit ANSI sequence, covering all mouse event modes (X10/buttons/all-motion/SGR). Works in conjunction with existing SIGINT/SIGTERM/SIGHUP/beforeExit signal handlers from #252.

TEST

Closes #838