feat(assets): add 3D-to-2D sprite render pipeline and /render-sprite skill

Godot @tool render scene that takes a textured 3D model and produces
2D sprites at 1024/256/64 from 4 cardinal directions with outlines
applied at working resolution. Camera at "the angle" (-72.5deg ortho).
Includes two POC wall models with Nano Banana textures, CLI wrapper
script with headless import step, and .uid files added to gitignore.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/tooling/sprite_renderer/models/wall_bar_green.tscn

@@ -0,0 +1,15 @@
+[gd_scene load_steps=3 format=3]
+
+[ext_resource type="Texture2D" path="res://tooling/sprite_renderer/textures/wall_bar_green_panels.png" id="1_wall_texture"]
+
+[sub_resource type="BoxMesh" id="BoxMesh_wall"]
+size = Vector3(1.0, 0.8, 0.2)
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_wall"]
+albedo_texture = ExtResource("1_wall_texture")
+metallic = 0.0
+roughness = 0.9
+
+[node name="WallBarGreen" type="MeshInstance3D"]
+mesh = SubResource("BoxMesh_wall")
+surface_material_override/0 = SubResource("StandardMaterial3D_wall")

client/tooling/sprite_renderer/models/wall_structural.tscn

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+[gd_scene load_steps=3 format=3 uid="uid://cyh0xf1nv2j3e"]
+
+[ext_resource type="Texture2D" uid="uid://bgn5kvwjdqrx0" path="res://tooling/sprite_renderer/textures/wall_institutional_era1.png" id="1_wall_texture"]
+
+[sub_resource type="BoxMesh" id="BoxMesh_wall"]
+size = Vector3(1.0, 0.8, 0.2)
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_wall"]
+albedo_texture = ExtResource("1_wall_texture")
+metallic = 0.0
+roughness = 0.9
+
+[node name="WallStructural" type="MeshInstance3D"]
+mesh = SubResource("BoxMesh_wall")
+surface_material_override/0 = SubResource("StandardMaterial3D_wall")