Summary

• Assign unique IDs to timeline notes (note-{paragraph_id}) instead of empty strings, so each note can be individually tracked
• Improve scroll tracking to ignore hidden horizontal view duplicates by checking element dimensions before processing intersection events
• Change scoring algorithm to prefer cards that contain the viewport center, ensuring small cards like notes are properly highlighted

Test plan

• Navigate to a project page with a timeline containing notes
• Scroll slowly through the timeline cards
• Verify each card (including notes) highlights its corresponding mini-nav dot
• Scroll quickly up and down
• Verify only one dot is highlighted at a time

Fixes #609

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