fix(native): silence standard library logs (#1425)

## Summary
- install a root `std_options.logFn` that discards `std.log` output
- leave Zig's default compile-time log level unchanged
- keep explicit OpenTUI `logger.logMessage` output flowing through the
existing JavaScript callback

## Why
OpenTUI imports native dependencies such as Ghostty into its Zig root
module. Their `std.log` calls otherwise use Zig's default stderr logger,
bypass the renderer, and can corrupt the terminal display. OpenTUI
already has a separate explicit logger for messages intended for
JavaScript and file logging, so standard-library logs should not write
directly to the host terminal.

## Testing
- `zig fmt --check packages/native/src/lib.zig`
- release `bun run build` from `packages/core`
- `bun run test:native` from `packages/core` (2066 passed, 8 skipped)