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/wire.wgsl

@@ -35,8 +35,15 @@ struct InstanceIn {
     @location(6) pattern_length: f32,
     @location(7) pat0:           vec4<f32>,
     @location(8) pat1:           vec4<f32>,
+    @location(9) draw_depth:     f32,
 }
 
+// Draw-order depth bias: shifts clip-space z so 2D entities of different
+// types order against each other through the shared LessEqual depth test.
+// draw_depth is signed (-1,1): front → positive → smaller z → drawn on top;
+// 0.0 = neutral (real depth). Depth32Float gives ample precision.
+const DRAW_ORDER_BIAS: f32 = 0.001;
+
 struct VertexOut {
     @builtin(position)              clip_pos:       vec4<f32>,
     @location(0)                    color:          vec4<f32>,
@@ -111,6 +118,7 @@ struct VertexOut {
 
     var out: VertexOut;
     out.clip_pos       = final_clip;
+    out.clip_pos.z     = out.clip_pos.z - in.draw_depth * DRAW_ORDER_BIAS * out.clip_pos.w;
     out.color          = in.color;
     out.distance       = mix(in.distance_a, in.distance_b, which_end);
     out.pattern_length = in.pattern_length;