Add boat click/tap detection

[nyan-dev]

Epic: E4 — Discover wishes and boat interaction
Type: Story
Area: Frontend
Priority: P1
Size: S

Implement hit detection on the water canvas so that clicking or tapping a boat triggers the wish discovery flow. The detection must work with both mouse clicks and touch events. The target area must be generous enough for comfortable mobile tapping.

Success criteria:

• Clicking a boat opens the wish discovery modal
• Touch-tapping a boat opens the wish discovery modal
• Tap target is at least 44px on mobile
• Non-boat clicks on the water do nothing (no false triggers)
• Keyboard focus can reach boats for accessibility