iter-png-3/o4-mini / tier-3-butt-hinge

```openscad
// Small butt hinge in open 180° configuration

module leaf(side=1) {
  // side = -1 for left leaf, +1 for right leaf
  difference() {
    union() {
      // leaf plate
      translate([ side == 1 ? 0 : -25, -15, 0 ])
        cube([25, 30, 2]);
      // knuckle barrels (outer)
      for (ypt = side == 1 ? [-6, 6] : [-12, 0, 12]) {
        translate([0, ypt, 6])
          rotate([-90, 0, 0])
            cylinder(h=6, r=4, center=true);
      }
    }
    // knuckle barrel inner holes
    for (ypt = side == 1 ? [-6, 6] : [-12, 0, 12]) {
      translate([0, ypt, 6])
        rotate([-90, 0, 0])
          cylinder(h=6, r=2.3, center=true);
    }
    // M3 countersunk screw holes
    for (ypt = [-8, 0, 8]) {
      // countersink: 6mm dia at surface → 3.2mm dia at 1mm depth
      translate([side*20, ypt, 1])
        cylinder(h=1, r1=1.6, r2=3, center=false);
      // through hole 3.2mm dia full thickness (2mm)
      translate([side*20, ypt, 0])
        cylinder(h=2, r=1.6, center=false);
    }
  }
}

// left leaf (x<0)
leaf(-1);
// right leaf (x>0)
leaf(1);

// hinge pin
translate([0, 0, 6])
  rotate([-90, 0, 0])
    cylinder(h=32, r=2, center=true);
```