Platformer: add physics-based runner jump arcs

[smcga]

Motivation

• The runner previously snapped vertically between platform heights, producing jarring "teleport" jumps instead of natural platformer arcs.
• Introduce a lightweight physics simulation so the mascot follows an arc on rises while preserving aesthetic bobbing and timing behavior.

Description

• Added a RunnerJumpState type and updateRunnerJumpState function implementing launch, gravity, fall-speed cap, and landing snap logic in src/renderer/effects/platformerScroll.ts.
• Integrated the jump-state into PlatformerScrollEffect.render, computing hop from the simulated y and resetting state on large time gaps/seeks to avoid glitches.
• Kept existing visual rendering (buildRunnerSprite bobbing/shading) and did not change effect params or registry keys so docs extraction remains stable.
• Updated unit tests in src/renderer/effects/platformerScroll.test.ts to cover jump-state launch, rise/fall behavior, and clean landing.

Testing

• Ran the focused unit tests with npm run test -- src/renderer/effects/platformerScroll.test.ts, and all tests passed.
• Ran the docs check with npm run docs:check, and the effects docs validation passed.

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Codex Task

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Project	Deployment	Actions	Updated (UTC)
codexperimental	Ready	Preview, Comment	Apr 8, 2026 1:04am