Improve package output for tree shaking

[krowvin]

Summary

Improves the library package output so consumers can import smaller parts of Groundwork without pulling the whole bundle:

• publish preserved ESM modules alongside the existing UMD build
• expose component, composite, hook, and utility subpaths
• move CSS to an explicit stylesheet entry
• lazy-load heavier footer image assets

Bundle check

Package pack size:

Package	Before	After
Packed tarball	4.65 MB	4.55 MB
Unpacked package	7.45 MB	7.05 MB

Representative downstream production bundle using Button from the package root:

Import	Before	Current	Gzip before	Gzip current
Button from @usace/groundwork	368.9 KB	240.2 KB	115.1 KB	75.1 KB

Validation

• clean npm ci
• npm test -- --run (2 files, 8 tests)
• npm run lint
• npm run build-lib
• npm run build
• npm pack and verified the expected ESM modules, UMD bundle, and explicit CSS entry
• installed the packed tarball in a clean React 19/Vite 8 consumer and completed a production build with zero vulnerabilities

The library and docs assets build successfully. The existing post-build route extraction still reports the missing direct @babel/parser development dependency, which is addressed separately by #300.

Related: #191, #218, #221, #179

[github-actions]

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