[M1-S3] Walk up hills and slide down steep slopes #29

User story

As a player, I want to walk over hills and skid down steep slopes, so that the world feels like Planet of Lana's terrain, not stairs.

Acceptance criteria

• Ground is the authored polyline: walk slopes ≤ 40° (green)
• Slopes > 40° (brown) slide, poncho flapping; jump off any time
• No jitter where slopes change; no staircase blocks

Design and references

Annotation colours: 04 – Collision and interaction annotation.

Dependencies

Needs the collision loader. Suggested owner: Vatsal (player and combat code).

Verification

Run every slope on the route at walk and run speed with the debug overlay on.