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

.gitignore

@@ -1,5 +1,5 @@
 homed
-waiter
+/waiter
 *.exe
 *.log
 *.test
@@ -14,3 +14,8 @@ internal/meta/
 
 *.hmap
 dev/
+
+# GUI
+cmd/gui/node_modules/
+cmd/gui/dist/
+