wgpu: overlay-line groups (stroke + dash, per-group dynamic uniform offset)

Ports GL OverlayRenderer's LineGroup API to WgpuOverlayRenderer. Each
group's segments are CPU-expanded into screen-space quads; the WGSL
fragment reproduces the GL pixel-distance stroke pick + arc-length
dash logic. One uniform slot per group, bound via dynamic offset so a
single bind-group services up to N groups.

No caller yet — sets up the API the wgpu measure tools (task #29) will
use. WgpuViewportWindow.setOverlayLines mirrors the GL viewport's
signature so the bonsai Measurement code can target either backend
through one interface.

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

src/ifcviewer-wgpu/WgpuViewportWindow.cpp

@@ -2831,6 +2831,12 @@ void WgpuViewportWindow::clearSectionPlanes() {
     if (isExposed()) requestUpdate();
 }
 
+void WgpuViewportWindow::setOverlayLines(
+        const std::vector<WgpuOverlayRenderer::LineGroup>& groups) {
+    overlays_.setOverlayLines(groups);
+    if (isExposed()) requestUpdate();
+}
+
 // Project a world point to LOGICAL pixel coords (Qt's mouse-event units).
 // Returns false if behind the camera.
 static bool projectWorldToLogicalScreen(const QMatrix4x4& vp,
@@ -3942,6 +3948,12 @@ void WgpuViewportWindow::render() {
     // surfaces. Visibility is driven by orbit/wheel UI handlers.
     overlays_.encodePivot(pass, overlay_frame, pivot_indicator_visible_);
 
+    // Overlay line groups (measurement / dimension annotation lines).
+    // Depth-tested against geometry so they hide behind closer surfaces;
+    // depth-write off so the corner gizmo + marquee can still draw over
+    // them on the resolved surface afterwards.
+    overlays_.encodeOverlayLines(pass, overlay_frame);
+
     wgpuRenderPassEncoderEnd(pass);
     wgpuRenderPassEncoderRelease(pass);