fix(db): harden sqlite3 signal handling

[tobwen]

Issue for this PR

Closes #17114

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This hardens opencode db when it launches the interactive sqlite3 shell.

The user-visible bug was that after leaving opencode db with Ctrl-C, the terminal could come back in a broken state and echo later input character-by-character on separate lines instead of returning cleanly to the shell.

This change fixes that by tightening the interactive sqlite3 signal and exit handling. It also closes the Bun SQLite handle in query mode with finally, handles sqlite3 spawn failures explicitly, preserves non-zero child exit codes, and avoids the global SIGHUP handler collapsing signal-derived exit status.

In short: the command now behaves much more predictably when sqlite3 is interrupted or terminated.

How did you verify your code works?

• Ran bun typecheck in packages/opencode
• Ran bun run build in packages/opencode
• Reproduced the issue by exiting opencode db with Ctrl-C and confirmed the shell returned cleanly instead of echoing later input character-by-character

Screenshots / recordings

Before

After

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR