feat: add multi-line highlights and comments support

[mattfinlayson]

Summary

Extend the annotation plugin to support highlighting text that spans multiple lines and attaching comments to those highlights.

Previously, the plugin only supported single-line ==highlights==. This PR adds multi-line %%highlight-start:ID%% / %%highlight-end:ID%% markers that work across paragraphs.

Changes

Multi-line Highlighting

• Auto-detection: createHighlightCommand now detects whether the selection spans multiple lines. Single-line uses ==text==, multi-line uses %%highlight-start:ID%%..%%highlight-end:ID%%
• Live preview rendering: Extended findHighlightsAndComments in extension.tsx to detect and render both marker formats
• Reading mode rendering: Updated postprocessor.tsx to parse multi-line highlights alongside single-line ones
• Styles: Added .multiline CSS class for block-level highlight display

Comments

• Comments on multi-line highlights use inline <!--comment--> after the end marker (consistent with existing single-line pattern)
• Existing CommentPopover UI works for both highlight types without changes

Editing & Management

• "Delete annotation at cursor" command: Removes markers and inline comments for both single-line and multi-line highlights
• "Clear all annotations" command: Strips all ==, %%, and <!----> markers from the document
• Comment editing via popover works for multi-line highlights via handleCommentUpdate

Version

• Bumped to 1.1.0

Test Plan

1. Open a note with multiple paragraphs
2. Select text across paragraph breaks → trigger "Highlight selection" → verify %%highlight-start:ID%% markers appear
3. Click the highlight in live preview → add a comment → verify <!--comment--> appears after end marker
4. Place cursor inside a highlight → "Delete annotation at cursor" → verify markers and comment are removed
5. "Clear all annotations" → verify all highlights and comments are stripped
6. Single-line ==highlights== still work as before