feat: monochrome black & white rebrand + new Pudu robots

- Convert site from royal-blue theme to black/white monochrome (desaturate
  all blue-hued colors; keep WhatsApp green and error red)
- Swap blue circular brand logo for mono YS mark; regenerate favicon/PWA icons
- Add 6 Pudu robots (CC1 Pro, MT1 Max, MT1 Vac, T600, T600 Underride, BG1 Pro)
- Fix favicon.ico to RGBA (Next 16 Turbopack decode) and Stripe apiVersion type

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/RobotModel.tsx

@@ -81,7 +81,7 @@ function BaseBodyMesh({ glbPath, primaryColor, visible }: { glbPath: string; pri
       if (child instanceof THREE.Mesh) {
         if (!child.material) {
           child.material = new THREE.MeshStandardMaterial({
-            color: '#96a2b6',
+            color: '#a6a6a6',
             metalness: 0.8,
             roughness: 0.2,
           });