perf(scene): extend viewport scissor to hatch / image / wipeout passes (Phase 1.4)

Wire pass already uses `WireModel.vp_scissor` to clip viewport-projected
geometry to its paper-space viewport rect; hatch / image / wipeout
passes drew across the whole canvas. When a future paper-space path
projects fills/images into a viewport, they would bleed past the
viewport frame.

Add `vp_scissor: Option<[f32; 4]>` to HatchModel and ImageModel
(mirroring WireModel), forward it through HatchGpu / ImageGpu, and add
per-pass `compute_*_scissors` / `set_scissor_rect` machinery. Factored
the wire-side scissor-projection math into a shared `project_scissor`
helper. Field defaults to None at every constructor site — no producer
sets it yet, so this is plumbing for the paper-viewport fill projection
that Phase 1.4 unblocks without changing current visual output.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/scene/render.rs

@@ -144,6 +144,9 @@ impl shader::Primitive for Primitive {
             pipeline.cached_epoch = cur_key;
         }
         pipeline.compute_wire_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
+        pipeline.compute_hatch_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
+        pipeline.compute_wipeout_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
+        pipeline.compute_image_scissors(self.uniforms.view_proj, clip_size.width, clip_size.height);
         if self.show_viewcube {
             pipeline.viewcube.upload(
                 queue,