release: v0.1.12 — accessibility, Zen mode, scroll sync v2, shortcutHelp plugin

feat(a11y): toolbar keyboard navigation (Arrow keys, Home, End)
feat(a11y): aria-live region for screen reader announcements on mode change
feat(a11y): enhance focus-visible style (outline-offset: 2px, hide on mouse focus)

feat(core): Zen mode (editor.toggleZen() / exec('zen'))
- Toggle with Ctrl+Shift+Z shortcut concept
- Auto-hide toolbar and statusbar, mouse to top edge reveals toolbar
- Centered editor pane with max-width constraint

feat(core): heading-aware scroll sync v2
- Sync preview scroll to nearest heading before cursor position
- Falls back to proportional sync when no headings found

feat(core): Word wrap toggle (editor.toggleWordWrap() / setWordWrap(bool))

feat(plugins): shortcutHelp preset plugin
- Press '?' to open keyboard shortcuts overlay panel
- Lists built-in + user-registered shortcuts
- Click overlay or press Escape to close

style: Zen mode CSS, sr-only class, focus-visible refinement

test: 3 new tests for Zen mode, WordWrap, shortcutHelp (535 total)

chore: bump version 0.1.11 → 0.1.12 across all files

site/docs.html

@@ -176,7 +176,7 @@
 
 <header class="docs-header">
   <h1><span class="grad">文档</span></h1>
-  <p class="sub">MetonaEditor v0.1.11 完整 API、配置与使用指南</p>
+  <p class="sub">MetonaEditor v0.1.12 完整 API、配置与使用指南</p>
 </header>
 
 <div class="container">
@@ -619,7 +619,7 @@ i18nUtils<span class="c-punc">.</span><span class="c-fn">formatDate</span><span
 
 <footer>
   <div class="container">
-    MetonaEditor v0.1.11 · <a href="https://git.metona.cn/MetonaTeam/MetonaEditor" target="_blank" rel="noopener">源码仓库</a> · MIT License
+    MetonaEditor v0.1.12 · <a href="https://git.metona.cn/MetonaTeam/MetonaEditor" target="_blank" rel="noopener">源码仓库</a> · MIT License
   </div>
 </footer>