Add native Windows build support

[skanga]

Summary

• add a native build.cmd entry point for Windows and document its use
• allow CGO_ENABLED=0 builds by falling back to JSON/JSONC-only syntax highlighting
• support Windows LSP file URIs, managed-download target triples, and portable installer tests

Why

The project did not compile with the standard Windows Go configuration because the tree-sitter dependency requires cgo. Windows path and executable assumptions also caused LSP tests and managed tooling behavior to fail.

Impact

Toast now builds as bin\toast.exe from cmd.exe without requiring a C compiler. When cgo is unavailable, JSON and JSONC retain syntax highlighting while tree-sitter-backed languages gracefully render as plain text.

Validation

• cmd /c build.cmd
• go test ./...
• go vet ./...
• git diff --check
• bin\toast.exe --version

[paradise-runner]

So excited to see the first external PR! Give me a little time to fire up my windows machine and validate the change before getting it merged in. Thanks so much!