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/components/journal/command-parser.ts

@@ -5,10 +5,14 @@
  * module and keep JournalInput small.
  */
 
+import type { IconTypes } from "solid-icons";
+
 export interface CompletionItem {
   label: string;
   kind: "command" | "value" | "no-results";
   insertText: string;
+  /** Optional icon rendered before the label in the completions dropdown. */
+  icon?: IconTypes;
 }
 
 export interface ParsedInput {