feat: resolve language servers from worktree PATH

[spotdemo4]

Closes #234.¹

Summary

Resolve oxlint and oxfmt from the worktree's PATH before falling back to the extension-managed npm installation.

The resolution order is now:

1. Explicit binary settings
2. Project-local package
3. Worktree PATH
4. Extension-managed npm installation

PATH binaries are launched directly with --lsp and the worktree shell environment. Configured environment variables are merged on top.

On Windows, PATH resolution is restricted to native .exe binaries to avoid selecting npm .cmd or .bat shims.

Validation

• cargo fmt --check
• cargo check --all-targets --all-features
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings
• cargo doc --no-deps --document-private-items

Footnotes

1. This pr was generated by GPT-5.6 Sol Fast. View the OpenCode conversation. ↩