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/shaders/face3d.wgsl

@@ -14,8 +14,9 @@ struct Uniforms {
 var<uniform> u: Uniforms;
 
 struct VertexIn {
-    @location(0) position: vec3<f32>,
-    @location(1) color:    vec4<f32>,
+    @location(0) position:   vec3<f32>,
+    @location(1) color:      vec4<f32>,
+    @location(2) draw_depth: f32,
 };
 
 struct VertexOut {
@@ -23,10 +24,15 @@ struct VertexOut {
     @location(0)       color:    vec4<f32>,
 };
 
+// Draw-order depth bias (see wire.wgsl). Signed draw_depth; 0.0 (3D mesh
+// faces) leaves real depth untouched; 2D fills / 3DFACE quads order by rank.
+const DRAW_ORDER_BIAS: f32 = 0.001;
+
 @vertex
 fn vs_main(v: VertexIn) -> VertexOut {
     var out: VertexOut;
     out.clip_pos = u.view_proj * vec4<f32>(v.position, 1.0);
+    out.clip_pos.z = out.clip_pos.z - v.draw_depth * DRAW_ORDER_BIAS * out.clip_pos.w;
     out.color    = v.color;
     return out;
 }