Scroll behaviour refinement

[nyan-dev]

Epic: E5 — Polish, responsiveness, and accessibility
Type: Story
Area: Frontend
Priority: P1
Size: S

Refine the scroll-based perspective reveal so that scrolling slightly rotates the well to show more water and boats. Per DESIGN.md, motion should be subtle, reveal more of the water surface, and preserve the retro fantasy feeling. Large camera spins or dramatic rotations are banned.

Success criteria:

• Scrolling reveals slightly more water surface
• Motion is subtle and readable
• Isometric illusion is preserved during scroll
• No dramatic 3D spinning or large camera swings
• Boat visibility increases as user scrolls