feat: refactor theme, add tailwind-scrollbar, and improve UI components

- Removed manual theme switching logic and ThemeProvider
- Installed and configured tailwind-scrollbar plugin
- Updated FileConverter and ConversionOptions to use shadcn Input
- Refactored FontSelector to use shadcn Tabs
- Simplified global styles and adjusted glassmorphic effects

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project
+
+Kit UI is a static-export toolkit (Next.js 16, React 19, TypeScript strict) with five browser-based tools: Color, Units, ASCII, Media, and Favicon. All heavy processing runs client-side via WebAssembly. Deployed at kit.pivoine.art.
+
+## Commands
+
+```bash
+pnpm dev          # Dev server with Turbopack (localhost:3000)
+pnpm build        # Static export to /out
+pnpm lint         # ESLint (next/core-web-vitals)
+pnpm postinstall  # Copies WASM binaries to public/wasm/ (runs automatically on install)
+```
+
+There are no test suites. Use `pnpm build` to verify changes compile correctly.
+
+## Architecture
+
+### Routing (App Router)
+
+```
+app/
+├── page.tsx              # Landing page (dark mode forced)
+├── (app)/layout.tsx      # Wraps all tools with Providers + AppShell
+├── (app)/color/          # Color manipulation (@valknarthing/pastel-wasm)
+├── (app)/units/          # Unit converter (187+ units, 23 categories)
+├── (app)/ascii/          # ASCII art (373 figlet fonts)
+├── (app)/media/          # File converter (FFmpeg + ImageMagick WASM)
+└── (app)/favicon/        # Favicon/PWA asset generator
+```
+
+### Code Organization
+
+Each tool follows a mirrored structure across three directories:
+
+- **`app/(app)/{tool}/page.tsx`** — Route entry point
+- **`components/{tool}/`** — UI components for the tool
+- **`lib/{tool}/`** — Business logic, WASM wrappers, stores, and utilities
+- **`types/`** — Shared TypeScript definitions
+
+Shared UI primitives live in `components/ui/` (shadcn/ui, customized with glassmorphic styling). Layout shell in `components/layout/`.
+
+### State Management (three layers)
+
+1. **URL params** — Primary for shareable state (`useSearchParams` / `useRouter().push`)
+2. **React Query** — Async WASM computations with caching
+3. **Zustand** — Per-tool client stores in `lib/{tool}/`
+4. **localStorage** — Persistence for theme, favorites, history
+
+### WASM Integration
+
+WASM modules (FFmpeg, ImageMagick, pastel-wasm) are lazy-loaded on first use. Binaries live in `public/wasm/` and are copied there by the postinstall script — don't move them manually. WASM logic is browser-only; do not attempt to run it in Node.
+
+## Conventions
+
+- **`'use client'`** only where needed (WASM, browser APIs, interactive state). Default to RSC.
+- **Styling**: Tailwind CSS 4 with CSS-first config in `app/globals.css`. Use `cn()` from `lib/utils/cn.ts` for conditional classes. Use `@utility glass` for glassmorphic effects and gradient utilities (`gradient-purple-blue`, etc.).
+- **Icons**: Lucide React exclusively.
+- **Imports**: Use `@/` path alias (resolves to project root).
+- **Components**: shadcn/ui from `components/ui/` as building blocks.
+- **Logic/UI separation**: Business logic in `lib/`, UI in `components/`. Keep them separate.
+
+## Deployment
+
+Static export (`output: 'export'` in next.config.ts) served by Nginx via Docker. No Node.js runtime in production.
+
+```bash
+docker build -t kit-ui .
+docker run -p 80:80 kit-ui
+```
+
+## PWA
+
+Service worker at `public/sw.js` pre-caches core assets and WASM binaries. Manifest generated from `app/manifest.ts` (force-static). Cache version: `kit-ui-v1`.