Preview Gallery

/preview renders an HTML page listing annotated images grouped by series.

Implementation outline (handlePreview):

1. Walk output/ recursively.
2. Select PNG files whose path includes /annotated/.
3. Extract series (first path segment) and address (filename sans extension).
4. Collect modification time and relative path.
5. Group by series, sort each group by descending modification time.
6. Render a Go html/template with a client-side JavaScript filter.

Each figure shows:

• Image (square container with object-fit: contain)
• Address (EIP-55 case)
• Timestamp (mod time formatted YYYY-MM-DD HH:MM:SS)