fix: Remove unused variable warning and add release build script

- Fix unused `project_path` parameter warning in make_executable()
- Add build-release.sh for automated binary packaging
- Update .gitignore to exclude release artifacts
- Support cross-compilation for Linux and Windows binaries

Release artifacts are now built with ./build-release.sh and uploaded
to Gitea releases separately, keeping the git repo clean.

.gitignore

@@ -22,6 +22,11 @@ Cargo.lock
 *.so
 *.exe
 
+# Release packaging (uploaded to releases, not checked in)
+/release-artifacts/
+*.tar.gz
+*.zip
+
 # OS
 Thumbs.db
 .AppleDouble