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

.github/workflows/ci.yml

@@ -0,0 +1,46 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [16.x, 18.x, 20.x]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Type check
+        run: npm run typecheck
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Run tests
+        run: npm test
+
+      - name: Build
+        run: npm run build
+
+      - name: Upload coverage
+        uses: actions/upload-artifact@v4
+        if: always()
+        with:
+          name: coverage-${{ matrix.node-version }}
+          path: coverage/