feat: GPU scissor rect for paper-space viewport wires

Viewport-projected wires now clip at pixel level to their viewport boundary.

- WireModel.vp_scissor: Option<[f32; 4]> — paper-space bbox set on projection
- WireGpu.vp_scissor carries it through to the draw loop
- Pipeline.compute_wire_scissors() converts paper→NDC→pixel each frame
- render() calls set_scissor_rect() per wire, reset after viewport group
- INTEGRATION_GAPS.md: Viewport ⚠️ → ✅, all 51 gaps resolved

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scene/tessellate.rs

@@ -105,6 +105,7 @@ pub fn tessellate(
             key_vertices: te.key_vertices,
             aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
                 };
             }
 
@@ -134,6 +135,7 @@ pub fn tessellate(
                             key_vertices: te.key_vertices,
                             aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
                         };
                     }
                     _ => {}
@@ -161,6 +163,7 @@ pub fn tessellate(
                         key_vertices,
                         aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
                     };
                 }
             }
@@ -186,6 +189,7 @@ pub fn tessellate(
                         key_vertices,
                         aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
                     };
                 }
             }
@@ -217,6 +221,7 @@ pub fn tessellate(
                     key_vertices,
                     aabb: WireModel::UNBOUNDED_AABB,
                     plinegen: true,
+            vp_scissor: None,
                 };
             }
 
@@ -243,6 +248,7 @@ pub fn tessellate(
                     aci: 0,
                     key_vertices,
                     plinegen: false,
+            vp_scissor: None,
                     aabb: WireModel::UNBOUNDED_AABB,
                 };
             }
@@ -274,6 +280,7 @@ pub fn tessellate(
         key_vertices,
         aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
     }
 }
 
@@ -330,6 +337,7 @@ pub fn tessellate_dimension(
         key_vertices,
         aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
     }];
 
     if let Some(text) = dimension_text_entity(dim) {
@@ -379,6 +387,7 @@ fn tessellate_leader(
             key_vertices: vec![],
             aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
         }];
     }
 
@@ -448,6 +457,7 @@ fn tessellate_leader(
         key_vertices,
         aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
     }]
 }
 
@@ -558,6 +568,7 @@ fn tessellate_multileader(
             key_vertices: key_verts,
             aabb: WireModel::UNBOUNDED_AABB,
             plinegen: true,
+            vp_scissor: None,
     }];
 
     // Render text content as MText wire