- Add new unit sprite sheet (advancewars-units.png/psd)
- Slow down all battle animations for better readability:
- Attack, flash, death, and delay timings increased
- Unit movement animation duration increased (70→180ms)
- Explosion animation slowed down
- Post-turn wait time increased (140→300ms)
- Merge props and units into shared Y-sorted "actors" depth band
- Buildings and units now sort correctly by screen row
- Move/attack overlays remain below actors for proper decal rendering
