feat: v0.2.1 — reference links, context menu, RTL, ja/ko, regex search, hooks, copy API

## Added
- Reference link/image resolution: [text][ref] + ![alt][ref] with [ref]: url definitions
- Right-click context menu: undo/redo/cut/copy/paste/selectAll + custom items
- RTL CSS layout support for Arabic, Hebrew, Persian etc.
- Japanese (ja) and Korean (ko) locales with 60+ keys each
- Divider position localStorage persistence
- Regex search toggle in search/replace panel
- Export HTML with embedded CSS styles
- beforeChange / afterChange lifecycle hooks (instance + global)
- copyAsMarkdown() / copyAsHTML() clipboard APIs
- CHANGELOG.md, CONTRIBUTING.md, CI workflow (.github/workflows/ci.yml)
- 2 new test suites: index.test.ts, styles.test.ts (684 total tests, +74)

## Changed
- autoSave plugin: closure-based state per instance instead of this context
- Plugin install() now receives options as second argument
- RTL locale detection: now uses language prefix (ar-SA → RTL)
- Rollup dev mode: only builds UMD format
- prepublishOnly now includes typecheck + test
- Version bumped to 0.2.1

## Fixed
- [text][ref] now correctly renders as link (was raw text)
- ![alt][ref] no longer produces empty src
- autoSave plugin state isolation across multiple editor instances
- Footnote definitions no longer consumed by refDef handler

CONTRIBUTING.md

@@ -0,0 +1,147 @@
+# Contributing to MetonaEditor
+
+Thanks for your interest in contributing! This document outlines the development workflow and conventions.
+
+## Prerequisites
+
+- Node.js >= 16.0.0
+- npm >= 8.0.0
+
+## Setup
+
+```bash
+git clone https://git.metona.cn/MetonaTeam/MetonaEditor.git
+cd MetonaEditor
+npm install
+```
+
+## Development
+
+```bash
+# Start dev server with hot reload (port 3001)
+npm run dev
+
+# Run tests in watch mode
+npm run test:watch
+
+# Type check
+npm run typecheck
+
+# Lint
+npm run lint
+npm run lint:fix
+
+# Format
+npm run format
+```
+
+## Project Structure
+
+```
+src/
+├── index.ts       # Entry point, global API
+├── core.ts        # MarkdownEditor class
+├── parser.ts      # Markdown parser (tokenizer + renderer)
+├── plugins.ts     # Plugin system & 6 presets
+├── themes.ts      # Theme system
+├── i18n.ts        # Internationalization
+├── styles.ts      # CSS-in-JS injection
+├── constants.ts   # Types, defaults, configs
+├── utils.ts       # Utility functions
+├── animations.ts  # Animation metadata
+├── icons.ts       # Toolbar SVG icons
+└── locales.ts     # Translation data
+
+tests/
+├── parser.test.ts
+├── core.test.ts
+├── plugins.test.ts
+├── themes.test.ts
+├── i18n.test.ts
+├── utils.test.ts
+├── animations.test.ts
+├── index.test.ts
+└── styles.test.ts
+
+site/
+├── index.html     # Landing page
+├── demo.html      # Full-featured demo
+└── docs.html      # API documentation
+```
+
+## Code Conventions
+
+### TypeScript
+- **Strict mode** is enabled — all code must pass `tsc --noEmit`.
+- Export types explicitly. Avoid `any` where possible.
+- Use `interface` for object shapes, `type` for unions/primitives.
+
+### Style
+- Run `npm run format` before committing (uses Prettier).
+- Follow existing comment patterns: JSDoc `/** */` for public APIs, `//` for inline notes.
+- Keep functions focused and under ~60 lines where practical.
+
+### Testing
+- **Every new feature must include tests.**
+- Test files mirror source structure: `src/foo.ts` → `tests/foo.test.ts`.
+- Use descriptive test names: `('does X when Y')`.
+- Run the full suite before submitting: `npm test`.
+
+### Commits
+- Use conventional commit messages:
+  - `feat: add reference link resolution`
+  - `fix: autoSave plugin state conflict`
+  - `docs: update API reference`
+  - `test: add index.ts global API tests`
+  - `chore: optimize rollup dev build`
+
+## Building
+
+```bash
+# Production build (all formats)
+npm run build
+
+# Output in dist/
+# ├── metona-editor.js        UMD
+# ├── metona-editor.min.js    UMD minified
+# ├── metona-editor.esm.js    ES Module
+# ├── metona-editor.cjs.js    CommonJS
+# └── metona-editor.d.ts      TypeScript declarations
+```
+
+## Plugin Development
+
+Plugins follow a simple convention:
+
+```typescript
+const myPlugin = {
+  name: 'myPlugin',
+  version: '1.0.0',
+  description: 'Description of my plugin',
+  depends: [],        // optional: plugin names this depends on
+  priority: 50,       // optional: for topological sort ordering
+
+  install(editor, options?) {
+    // Called when plugin is installed
+    // Use editor.on() to subscribe to events
+    // Return a Promise for async initialization
+  },
+
+  destroy(editor) {
+    // Called when plugin is uninstalled
+    // Clean up event listeners, timers, DOM nodes
+  },
+};
+```
+
+## Releasing
+
+1. Update version in `package.json` and `src/index.ts` (`VERSION` constant).
+2. Update `CHANGELOG.md`.
+3. Run full test suite: `npm test`.
+4. Build: `npm run build`.
+5. Publish: `npm publish`.
+
+## Questions?
+
+Open an issue at [git.metona.cn/MetonaTeam/MetonaEditor/issues](https://git.metona.cn/MetonaTeam/MetonaEditor/issues).