fix(opentui): handle SIGINT to prevent garbled output on Windows

[Arthur742Ramos]

Fixes #10414

Summary

• Adds SIGINT handler in App component to properly cleanup renderer on Ctrl+C
• Prevents 60 FPS render loop from continuing to output ANSI sequences after exit

Verification

1. Ran bun dev on Windows
2. Pressed Ctrl+C
3. Terminal exited cleanly without garbled escape sequence output

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Related PR Found:

• PR fix(opencode): disable mouse tracking on exit #8355 - "fix(opencode): disable mouse tracking on exit"
  • fix(opencode): disable mouse tracking on exit #8355
  • Why it's related: This PR also addresses cleanup and proper exit handling for the terminal UI, which is related to the signal handling and renderer cleanup being addressed in PR fix(opentui): handle SIGINT to prevent garbled output on Windows #10433. Both deal with gracefully shutting down terminal features to prevent garbled output.

[Arthur742Ramos]

The test failures are pre-existing issues on the dev branch (e2e tests in packages/app are failing). This PR only modifies TUI code in packages/opencode/src/cli/cmd/tui/app.tsx which is not covered by those e2e tests. The typecheck workflow passes.