fix(mobile): improve viewport framing and ignore screenshots

Adjust 2D bounds padding and portrait 3D FOV behavior to reduce mobile cropping, and ignore local screenshots artifacts in git.

.gitignore

@@ -0,0 +1 @@
+screenshots/

src/geometry.js

@@ -65,11 +65,13 @@ export function mechanismBounds() {
     maxX = Math.max(maxX, p.x);
     maxY = Math.max(maxY, p.y);
   }
-  const pad = 30;
+  // Increase padding to account for full range of motion and potential parameter changes
+  const padX = 50;
+  const padY = 60;
   return {
-    minX: minX - pad,
-    minY: minY - pad,
-    maxX: maxX + pad,
-    maxY: maxY + pad,
+    minX: minX - padX,
+    minY: minY - padY,
+    maxX: maxX + padX,
+    maxY: maxY + padY,
   };
 }

src/renderer3d.js

@@ -201,7 +201,24 @@ export function create3DRenderer(mountEl) {
     const width = Math.max(1, mountEl.clientWidth || 1);
     const height = Math.max(1, mountEl.clientHeight || 1);
     renderer.setSize(width, height, false);
-    camera.aspect = width / height;
+    
+    const aspect = width / height;
+    camera.aspect = aspect;
+
+    // Adjust FOV for portrait mode to keep the subject in view
+    // Base FOV is 42 degrees for landscape (aspect >= 1)
+    // For portrait, we increase FOV to maintain horizontal coverage
+    if (aspect < 1) {
+      const baseFovRad = (42 * Math.PI) / 180;
+      // Calculate horizontal FOV for aspect=1
+      const hFov = 2 * Math.atan(Math.tan(baseFovRad / 2) * 1);
+      // Calculate new vertical FOV to match that horizontal coverage
+      const newVFovRad = 2 * Math.atan(Math.tan(hFov / 2) / aspect);
+      camera.fov = (newVFovRad * 180) / Math.PI;
+    } else {
+      camera.fov = 42;
+    }
+
     camera.updateProjectionMatrix();
   }