feat: add package/build.sh cross-platform build script

- build.sh supports linux/amd64, linux/arm64, darwin/amd64, darwin/arm64,
  windows/amd64, and 'all' for matrix build
- Components: homed (CGO, Linux/macOS-only), waiter (all platforms), gui
- Platform matrix documented in script header
- waiter: extract setRawMode into rawmode_linux.go + rawmode_other.go for
  cross-platform support
- Add cmd/gui/node_modules/ and dist/ to .gitignore
- Fix .gitignore waiter pattern to not ignore cmd/waiter/ directory

cmd/waiter/rawmode_other.go

@@ -0,0 +1,9 @@
+//go:build !linux
+
+package main
+
+import "fmt"
+
+func setRawMode(fd int) (func(), error) {
+	return func() {}, fmt.Errorf("raw terminal mode not supported on this platform")
+}