Fix gallery masonry layout gaps with randomized sequential loading

- Add width/height dimensions to all 79 images in gallery.json
- Replace FIFO skeleton queue with ID-keyed skeleton map for zero layout shift
- Create dimension-matched skeletons using actual image aspect ratios
- Shuffle gallery order randomly on each page refresh (Fisher-Yates)
- Load images sequentially in shuffled order for top-to-bottom grid fill
- Replace byte-level Streams API progress with organic simulated progress
- Randomize progress checkpoints, deceleration speed, and stall points
- Fix lightbox click handler to use dynamic index lookup

Author: sin4ch