webclient: refresh vendored gnexus-ui-kit to v1.0.0 + dist-css wiring ...

- vendor 0.2.0 (snapshot d640a9e, ~93M with demo/node_modules) replaced
  with a clean 1.0.0 subset (4.5M): src/{js,scss,vue}, dist/{css,vue,js},
  dist assets (IBM Plex Mono fonts), docs, README/CLAUDE/AGENTS
- kit component CSS now consumed as prebuilt dist (import
  'gnexus-ui-kit/css' before app styles): kit 1.0 _fonts.scss uses
  relative url() for IBM Plex Mono, which breaks source compilation;
  the bundler resolves them into vendor dist/assets
- main.scss drops @use 'kit' as * (still broken by the font urls);
  kit-deps stays for focus_ring + SCSS tokens in app.scss and scoped
  blocks
- app.scss scrollbar block removed (kit.css 1.0 ships identical styles)
- vite.config: dead @kit alias removed; brand-new 'gnexus-ui-kit/css'
  alias now consumed
- product dist/ rebuilt (tracked: served by backend, deployed from git)

Verified: vitest 111 passed, vite build OK (ttf emitted, hashed),
preview screenshot renders dark kit theme with new density