Add mount rider bob and hoofbeat sounds, improve world map

- Rider character bobs with mount's run animation (sinusoidal, 0.12u amplitude)
- Mount hoofbeat footstep sounds triggered at 4 points per animation cycle
- M key opens map directly to player's current zone instead of continent
- Mouse wheel scroll zooms map in/out between world, continent, and zone views
- Fog of war darkens unexplored zones on continent view, clears on visit

include/rendering/renderer.hpp

@@ -252,6 +252,11 @@ private:
     uint32_t footstepLastAnimationId = 0;
     float footstepLastNormTime = 0.0f;
     bool footstepNormInitialized = false;
+
+    // Mount footstep tracking (separate from player's)
+    uint32_t mountFootstepLastAnimId = 0;
+    float mountFootstepLastNormTime = 0.0f;
+    bool mountFootstepNormInitialized = false;
     bool sfxStateInitialized = false;
     bool sfxPrevGrounded = true;
     bool sfxPrevJumping = false;