feat(bindings): expose terminal backend selection

[cpendery (cpendery)]

Summary

• expose backend defaults and per-call overrides in Python and Node
• include libghostty in both native extensions and their generated declarations
• install Zig 0.16 throughout release builds and stop publishing unsupported Windows ARM64 artifacts

Validation

• 49 Node tests
• 80 Python tests
• generated Python/Node declaration checks
• actionlint for CI and release workflows

Signed-off-by: cpendery cpendery@vt.edu --- _{Stack created with GitHub Stacks CLI • Give Feedback 💬}