feat(ui): replace unicode icons with solid-icons

Swap emoji and unicode glyphs for Tabler components so icons inherit
currentColor and font-size and render consistently across platforms.

- add src/components/doc-icons.ts to resolve doc-entry frontmatter icon
  keys to components; frontmatter now stores semantic keys
- replace the align-*.png assets with TbOutlineAlign* icons
- render RevealManager action SVGs as components instead of injected
  innerHTML strings
- carry completion icons via an optional CompletionItem.icon field

src/doc-entries/md-dice.md

@@ -1,6 +1,6 @@
 ---
 tag: md-dice
-icon: 🎲
+icon: dice
 title: 骰子组件
 ---
 
@@ -23,7 +23,7 @@ title: 骰子组件
 :md-dice[2d20k1+5]{key="advantage"}
 ```
 
-点击 🎲 图标执行投掷，显示结果；点击文字重置为原始公式。
+点击骰子图标执行投掷，显示结果；点击文字重置为原始公式。
 
 ## 属性