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/journal-set.md

@@ -1,6 +1,6 @@
 ---
 tag: journal-set
-icon: 🔢
+icon: set
 title: 变量系统
 description: 在文档中声明变量和标签，通过 /set 命令设置变量值，自动计算派生变量和标签效果。
 syntax: '```yaml role=declare'