feat(pick): select frame-like entities by clicking inside them

Images, OLE frames, wipeouts, underlays, paper-space viewports and
drawing-view borders were selectable only on their outline. Each now
carries an interior pick surface (pick_tris over its rectangle, or the
triangulated clip polygon for a clipped underlay), ranked below edge
and fill hits so content drawn inside still wins the click. The
layout's own sheet ("overall") viewport is excluded — identified by
the Layout object's viewport link, since DWG files carry viewport
id = 0 and some center the sheet viewport off-origin — or it would
swallow every click over the real viewports beneath it. Drawing-view
borders draw nothing normally; they emit an invisible pick-only wire
whose rect outline appears while selected.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scene/convert/tessellate.rs

@@ -1392,12 +1392,41 @@ pub fn tessellate(
     // f64 for the WireModel's double-single-era snap buffer.
     let snap_pts: Vec<(glam::DVec3, SnapHint)> =
         snap_pts.into_iter().map(|(p, h)| (p.as_dvec3(), h)).collect();
+    // A paper-space viewport is a window, not a wireframe: give it an interior
+    // pick surface so a click anywhere inside the frame selects it. Ranked
+    // below edge and fill hits, so content drawn inside still wins the click.
+    // The sheet ("overall") viewport is the layout's own invisible camera
+    // frame covering the whole page — never pickable, or it would swallow
+    // every click over the real viewports beneath it. It is identified by the
+    // Layout object's viewport link (authoritative — DWG files carry id = 0
+    // and this file class centres the sheet viewport off-origin, so neither
+    // the id nor the geometry heuristic alone is reliable), with
+    // `is_content_viewport` as the fallback classifier.
+    let is_sheet_vp = |vp: &acadrust::entities::Viewport| {
+        let h = vp.common.handle;
+        document.objects.values().any(|obj| {
+            matches!(obj, acadrust::objects::ObjectType::Layout(l) if l.viewport == h)
+        }) || !crate::scene::Scene::is_content_viewport(vp)
+    };
+    let (pick_tris, pick_tris_low) = match entity {
+        EntityType::Viewport(vp) if !is_sheet_vp(vp) => {
+            let (cx, cy, cz) = (vp.center.x, vp.center.y, vp.center.z);
+            let (hw, hh) = (vp.width / 2.0, vp.height / 2.0);
+            points_to_ds(crate::entities::common::quad_pick_tris(&[
+                [cx - hw, cy - hh, cz],
+                [cx + hw, cy - hh, cz],
+                [cx + hw, cy + hh, cz],
+                [cx - hw, cy + hh, cz],
+            ]))
+        }
+        _ => (Vec::new(), Vec::new()),
+    };
     vec![WireModel {
         taper_widths: Vec::new(),
         world_width: 0.0,
         fill_is_3d: false,
-        pick_tris: Vec::new(),
-        pick_tris_low: Vec::new(),
+        pick_tris,
+        pick_tris_low,
             dash_from_start: false,
             dash_align_end: None,
             text_verts: Vec::new(),