fix: add plugin.json for Claude Code skill loading (#125)

Claude Code requires plugin.json (not just marketplace.json) to load
plugins. The plugin.json must include a "skills" field pointing to
the skill directory location.

Without this file, the plugin appears in `/plugins installed` but
the skill is not loaded into the prompt.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Viet Tran <viettranx@gmail.com>

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "ui-ux-pro-max",
+  "description": "UI/UX design intelligence. 50 styles, 21 palettes, 50 font pairings, 20 charts, 9 stacks (React, Next.js, Vue, Svelte, SwiftUI, React Native, Flutter, Tailwind, shadcn/ui). Actions: plan, build, create, design, implement, review, fix, improve, optimize, enhance, refactor, check UI/UX code. Projects: website, landing page, dashboard, admin panel, e-commerce, SaaS, portfolio, blog, mobile app, .html, .tsx, .vue, .svelte. Elements: button, modal, navbar, sidebar, card, table, form, chart. Styles: glassmorphism, claymorphism, minimalism, brutalism, neumorphism, bento grid, dark mode, responsive, skeuomorphism, flat design. Topics: color palette, accessibility, animation, layout, typography, font pairing, spacing, hover, shadow, gradient. Integrations: shadcn/ui MCP for component search and examples.",
   "version": "2.0.1",
-  "description": "Professional UI/UX design intelligence for AI coding assistants. Includes searchable databases of styles, colors, typography, charts, and UX guidelines for React, Next.js, Vue, Svelte, SwiftUI, React Native, Flutter, Tailwind, and shadcn/ui.",
   "author": {
     "name": "nextlevelbuilder"
   },