docs: split README into separate docs

Move tech stack, getting started, and gameplay sections into docs/
folder. Slim README down to a landing page with links.

README.md

@@ -4,58 +4,15 @@ A browser-based clone of the [Suika Game](https://en.wikipedia.org/wiki/Suika_Ga
 
 Built with [ClaudeKit](https://github.com/carlrannaberg/claudekit).
 
-## Tech Stack
-
-| Category | Tool | Version | Purpose |
-|----------|------|---------|---------|
-| **Runtime** | [Matter.js](https://brm.io/matter-js/) | ^0.20.0 | 2D rigid-body physics engine |
-| **Rendering** | Canvas2D | (built-in) | Fruit drawing, UI overlay, game-over screen |
-| **Build** | [Vite](https://vitejs.dev/) | ^8.0.4 | Dev server, ES module bundling, production builds |
-| **Testing** | [Vitest](https://vitest.dev/) | ^4.1.4 | Unit and integration tests |
-| **Language** | JavaScript (ES Modules) | — | Vanilla JS, no framework |
-| **Dev Tooling** | [ClaudeKit](https://github.com/carlrannaberg/claudekit) | — | Git hooks for linting, type-checking, testing, self-review |
-
-## Project Structure
-
-```
-src/
-  main.js          Entry point: initializes game, attaches event listeners
-  game.js          Game class: orchestrates engine, renderer, input, state
-  physics.js       Matter.js engine setup, world configuration, walls
-  renderer.js      Canvas2D rendering: fruits, walls, UI overlay
-  input.js         Mouse/touch input handling, drop control
-  fruits.js        Fruit definitions (sizes, colors, labels, progression)
-  merger.js        Collision detection callback, merge logic, scoring
-  constants.js     Game dimensions, physics tuning, timing constants
-  style.css        Page styling
-  *.test.js        Vitest test files
-index.html         Single HTML page with canvas element
-specs/             Feature and bugfix specifications
-```
-
-## Getting Started
+## Quick Start
 
 ```bash
 npm install
 npm run dev
 ```
 
-Open the URL shown in the terminal (default: http://localhost:5173).
+## Documentation
 
-## How to Play
-
-1. Move your mouse (or touch on mobile) to position the fruit
-2. Click/tap to drop it into the container
-3. When two identical fruits touch, they merge into the next larger fruit
-4. The fruit chain goes: Cherry → Strawberry → Grapes → Dekopon → Persimmon → Apple → Pear → Peach → Pineapple → Melon → Watermelon
-5. Game ends when fruits stack above the danger line
-
-## Scripts
-
-| Command | Description |
-|---------|-------------|
-| `npm run dev` | Start Vite dev server with HMR |
-| `npm run build` | Production build to `dist/` |
-| `npm run preview` | Preview the production build |
-| `npm test` | Run all tests once |
-| `npm run test:watch` | Run tests in watch mode |
+- [Getting Started](docs/getting-started.md) — Setup, scripts, and prerequisites
+- [Tech Stack](docs/tech-stack.md) — Dependencies, tools, and project structure
+- [Gameplay](docs/gameplay.md) — How to play and the full fruit chain