refactor: use applesauce helpers for highlight parsing

- Replace manual tag parsing with applesauce-core helper functions
- Use getHighlightText, getHighlightContext, getHighlightComment, etc.
- Add support for highlight comments in UI
- Extract author from attributions using proper helper
- Handle both event and address pointers correctly
- Add styling for highlight comments

This follows applesauce best practices and makes the code more robust.

src/types/highlights.ts

@@ -10,5 +10,6 @@ export interface Highlight {
   urlReference?: string // 'r' tag
   author?: string // 'p' tag with 'author' role
   context?: string // surrounding text context
+  comment?: string // optional comment about the highlight
 }