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/entities/ole2frame.rs

@@ -43,7 +43,14 @@ fn to_truck(ole: &Ole2Frame) -> TruckEntity {
     ];
     let center = glam::DVec3::new(cx, cy, z);
     TruckEntity {
-        pick_tris: Vec::new(),
+        // Interior pick surface: the frame selects on a click anywhere
+        // inside, not just on its border.
+        pick_tris: crate::entities::common::quad_pick_tris(&[
+            [x0, y0, z],
+            [x1, y0, z],
+            [x1, y1, z],
+            [x0, y1, z],
+        ]),
         object: TruckObject::Lines(pts),
         snap_pts: vec![(center, SnapHint::Center)],
         tangent_geoms: vec![],