Add 2D endless runner game with pickups and coyote time

- Platformer endless runner: fixed player x, world scrolls left
- Logarithmic speed curve: initial + factor * ln(1 + t / time_scale)
- Enemies stomped from above; side/bottom contact kills player
- Procedural level generation with StdRng seeded from SystemTime
- Object pooling via Vec::retain + frontier-based generator
- Coyote time: grace window after leaving platform edge
- Data-driven pickup system with trait-based effects (ActiveEffect)
  - Invulnerability, JumpBoost, ScoreMultiplier — extend via config
- Score accumulates with per-effect multiplier; stomp bonuses scaled
- Game over screen with score, best score, restart prompt
- HUD: score, speed bar, active effect timer bars

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "endless_runner"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+rand = "0.10.0"
+raylib = { version = "5.5.1", features = ["wayland"] }