docs: update README with Calculate tool and 8-tool count

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -13,7 +13,7 @@ Built with **Next.js 16**, **React 19**, and **Tailwind CSS 4**, Kit UI delivers
 
 ## 🚀 The Toolkit
 
-Kit UI currently ships **7 tools**:
+Kit UI currently ships **8 tools**:
 
 ### 🎨 [Color](./app/(app)/color) — Color Manipulation
 Modern color manipulation toolkit with palette generation and format conversion.
@@ -59,6 +59,13 @@ Visual editor for CSS `@keyframe` animations with live preview and export.
 - **Live Preview**: Real-time preview with speed control and element selector.
 - **Export**: Plain CSS or Tailwind v4 `@utility` format.
 
+### 🧮 [Calculate](./app/(app)/calculate) — Calculator & Grapher
+Advanced mathematical expression evaluator with an interactive function grapher.
+- **Full Math.js Engine**: Trig, logarithms, complex numbers, matrices, factorials, combinatorics, and more.
+- **Named Variables**: Define and reuse variables (`x = 5`) across expressions and graph functions.
+- **32 Quick-Insert Keys**: One-click constants (π, e, φ) and functions (sin, ln, gcd, nCr…).
+- **Interactive Graph**: Plot up to 8 simultaneous color-coded functions with pan (drag) and zoom (scroll); crosshair tooltip shows coordinates and per-function values.
+
 ---
 
 ## ✨ Core Features
@@ -80,6 +87,7 @@ Visual editor for CSS `@keyframe` animations with live preview and export.
 - **Styling**: [Tailwind CSS 4](https://tailwindcss.com) (CSS-first configuration)
 - **Animations**: [Framer Motion](https://www.framer.com/motion/)
 - **State Management**: [Zustand](https://github.com/pmndrs/zustand) & [React Query](https://tanstack.com/query)
+- **Math Engine**: [Math.js 15](https://mathjs.org) (expression evaluation, compilation cache)
 - **Icons**: [Lucide React](https://lucide.dev)
 - **Type Safety**: [TypeScript 5](https://www.typescriptlang.org)
 
@@ -90,7 +98,7 @@ Visual editor for CSS `@keyframe` animations with live preview and export.
 ```bash
 .
 ├── app/                  # Next.js App Router (Pages & Layouts)
-│   ├── (app)/            # Tool pages (color, units, ascii, media, favicon, qrcode, animate)
+│   ├── (app)/            # Tool pages (color, units, ascii, media, favicon, qrcode, animate, calculate)
 │   ├── manifest.ts       # PWA manifest generation
 │   └── api/              # Backend API routes
 ├── components/           # Reusable UI & Logic Components
@@ -101,6 +109,7 @@ Visual editor for CSS `@keyframe` animations with live preview and export.
 │   ├── favicon/          # Favicon-specific components
 │   ├── qrcode/           # QR code components
 │   ├── animate/          # CSS animation editor components
+│   ├── calculate/        # Calculator & grapher components
 │   └── ui/               # Base Atomic Components (Buttons, Cards, etc.)
 ├── lib/                  # Business Logic & Utilities
 │   ├── color/            # WASM wrappers & Color logic
@@ -109,7 +118,8 @@ Visual editor for CSS `@keyframe` animations with live preview and export.
 │   ├── media/            # FFmpeg & ImageMagick WASM orchestration
 │   ├── favicon/          # Favicon generation logic
 │   ├── qrcode/           # QR code generation logic
-│   └── animate/          # CSS builder, presets, and defaults
+│   ├── animate/          # CSS builder, presets, and defaults
+│   └── calculate/        # Math.js engine, graph sampler, Zustand store
 ├── public/               # Static assets & ASCII fonts
 ├── Dockerfile            # Multi-stage Docker build
 └── nginx.conf            # Production Nginx configuration