chore(release): prepare v0.1.9

[chaliy]

Summary

• Bump workspace version from 0.1.8 to 0.1.9
• Update CHANGELOG.md with all 50 changes since v0.1.8
• Highlight our first external contribution from Alexandru Chiculita (PR feat(python): add external function handler support #394: external function handler support for Python bindings)

Release highlights

• First external contribution! Alexandru Chiculita added external function handler support for the Python bindings — a milestone for the project
• Comprehensive security hardening: deep audit with 40+ fixes across VFS, parser, interpreter, network, and Python bindings
• HTTP, git, and Python features now enabled by default in the CLI
• Multi-byte UTF-8 safety across builtins (awk, tr, printf, expr)
• Python runtime improvements: GIL release, tokio runtime reuse, security config preservation

Test plan

• cargo fmt --check passes
• cargo clippy --all-targets --all-features -- -D warnings passes
• cargo test --all-features passes (84 passed, 0 failed)
• ruff check and ruff format --check pass
• CI green before merge
• After merge, CI auto-creates GitHub Release and publishes to crates.io + PyPI