feat(draworder): cross-type draw order + context menu

DRAWORDER now affects rendering immediately (bump geometry epoch so the
sort cache rebuilds) and front/back anchor to the block's full effective
sort range instead of only existing table entries, so bring-to-front
actually lands on top. The render fallback sorts table-absent entities by
their own handle.

Draw order now applies across entity types, not just within a type. A
per-entity draw-order rank (SortEntitiesTable override or own handle,
ranked per block) is encoded as a small signed clip-z bias in the wire,
hatch, image, and 3DFACE pipelines. The shared LessEqual depth buffer then
orders fills, lines, rasters and 2D solids against each other regardless of
pass order — without touching model coordinates. 3D meshes keep real
geometric depth; wipeouts stay always-on-top.

Adds a Draw Order submenu to the viewport context menu (Bring to Front,
Send to Back, Bring Above/Send Under Object). The above/under items run an
interactive reference-object pick, then reorder the captured selection.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/pipeline/hatch_batched_gpu.rs

@@ -64,7 +64,10 @@ pub struct HatchInstance {
     pub boundary_count: u32,        //  92
     pub family_offset: u32,         //  96
     pub family_count: u32,          // 100
-    pub _pad0: [u32; 2],            // 104  (pad to 112 = 16-byte stride)
+    /// Signed draw-order depth (-1,1); 0.0 = neutral. Applied as a clip-z
+    /// bias in the vertex shader so this fill orders against other types.
+    pub draw_depth: f32,            // 104
+    pub _pad0: u32,                 // 108  (pad to 112 = 16-byte stride)
 }
 
 const _: () = assert!(std::mem::size_of::<HatchInstance>() == 112);
@@ -274,7 +277,8 @@ impl HatchBatchedGpu {
                     boundary_count,
                     family_offset,
                     family_count,
-                    _pad0: [0; 2],
+                    draw_depth: h.draw_depth,
+                    _pad0: 0,
                 });
                 continue;
             }
@@ -312,7 +316,8 @@ impl HatchBatchedGpu {
                 boundary_count,
                 family_offset,
                 family_count,
-                _pad0: [0; 2],
+                draw_depth: h.draw_depth,
+                _pad0: 0,
             });
         }