fix: Keep tidal bulge aligned with Moon during Earth rotation

The tidal bulge was incorrectly rotating with Earth instead of
staying aligned with the Moon. Fixed by transforming the moon/sun
direction vectors from world space to object space using the
inverse of the mesh's rotation quaternion.

Now the bulge correctly points toward the Moon regardless of
Earth's rotation, as it should physically.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: cjw6k

tidal-harmonics/src/components/canvas/TidalEarth.tsx

@@ -1,6 +1,6 @@
 import { useRef, useMemo } from 'react';
 import { useFrame, useLoader } from '@react-three/fiber';
-import { TextureLoader, Vector3, Texture } from 'three';
+import { TextureLoader, Vector3, Texture, Quaternion } from 'three';
 import type { Mesh } from 'three';
 import { useCelestialPositions } from '@/hooks/useCelestialPositions';
 import { useScene } from '@/hooks/useScene';
@@ -92,9 +92,28 @@ export function TidalEarth() {
   );
 
   useFrame(({ clock }, delta) => {
-    // Update moon/sun directions (normalized)
-    uniforms.moonDirection.value.set(moon[0], moon[1], moon[2]).normalize();
-    uniforms.sunDirection.value.set(sun[0], sun[1], sun[2]).normalize();
+    // Earth rotation (do this first so we can use the rotation to transform directions)
+    if (meshRef.current && playing) {
+      meshRef.current.rotation.y += ROTATION_SPEEDS.EARTH * delta * speed;
+    }
+
+    // Transform moon/sun directions from world space to object space
+    // This ensures the tidal bulge always points toward the Moon regardless of Earth's rotation
+    const moonDir = new Vector3(moon[0], moon[1], moon[2]).normalize();
+    const sunDir = new Vector3(sun[0], sun[1], sun[2]).normalize();
+
+    if (meshRef.current) {
+      // Get inverse of mesh rotation to transform world -> object space
+      const inverseQuat = new Quaternion();
+      meshRef.current.getWorldQuaternion(inverseQuat);
+      inverseQuat.invert();
+
+      moonDir.applyQuaternion(inverseQuat);
+      sunDir.applyQuaternion(inverseQuat);
+    }
+
+    uniforms.moonDirection.value.copy(moonDir);
+    uniforms.sunDirection.value.copy(sunDir);
 
     // Pedagogical tidal amplitude for visible effect
     // Physical amplitude (0.53m / 6,371km = 8.3e-8) is invisible even at 50,000×
@@ -115,11 +134,6 @@ export function TidalEarth() {
     }
 
     uniforms.tidalAmplitude.value = amplitude;
-
-    // Earth rotation
-    if (meshRef.current && playing) {
-      meshRef.current.rotation.y += ROTATION_SPEEDS.EARTH * delta * speed;
-    }
   });
 
   return (