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>

.claude/skills/render-sprite/SKILL.md

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+---
+name: render-sprite
+description: >
+  Render a 3D model to 2D sprites via the Godot render pipeline. Produces
+  sprites at 3 resolutions (1024, 256, 64) from 4 cardinal directions (north,
+  east, south, west) with outline applied at working resolution. Use when the
+  user says "render sprite", "render model", "run the render pipeline",
+  "test the pipeline", "/render-sprite", or asks to render a specific model
+  (e.g., "render wall_structural"). Output: 12 PNG files in
+  client/tooling/sprite_renderer/output/.
+---
+
+## Render Pipeline
+
+Run the render script with the model name:
+
+```bash
+.claude/skills/render-sprite/scripts/render.sh <model_name>
+```
+
+### Available Models
+
+Models live at `client/tooling/sprite_renderer/models/<name>.tscn`. List them:
+
+```bash
+ls client/tooling/sprite_renderer/models/*.tscn | xargs -I{} basename {} .tscn
+```
+
+### Output
+
+12 files per model in `client/tooling/sprite_renderer/output/`:
+
+```
+<model>_north_1024.png   <model>_north_256.png   <model>_north_64.png
+<model>_east_1024.png    <model>_east_256.png    <model>_east_64.png
+<model>_south_1024.png   <model>_south_256.png   <model>_south_64.png
+<model>_west_1024.png    <model>_west_256.png    <model>_west_64.png
+```
+
+### After Rendering
+
+1. Read the 64x64 output files to visually inspect the runtime sprites
+2. Read the 256x256 files to check outline quality
+3. Report: does it read as the intended object at runtime scale?
+
+### Troubleshooting
+
+- **No output files**: Godot needs a display. If running headless, prefix with `xvfb-run`.
+- **Model not found**: Check the model .tscn exists in `models/` directory.
+- **Godot not found**: Pass path as second arg: `render.sh wall_structural /path/to/godot`
+
+### Adding New Models
+
+1. Create model scene at `client/tooling/sprite_renderer/models/<name>.tscn`
+2. Apply texture from `textures/` via StandardMaterial3D
+3. Run: `.claude/skills/render-sprite/scripts/render.sh <name>`

.claude/skills/render-sprite/scripts/render.sh

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+#!/bin/bash
+# Render a 3D model to 2D sprites at 3 resolutions from 4 cardinal directions.
+# Usage: render.sh <model_name> [godot_path]
+# Example: render.sh wall_structural
+set -euo pipefail
+
+MODEL_NAME="${1:?Usage: render.sh <model_name> [godot_path]}"
+GODOT="${2:-$HOME/bin/godot}"
+REPO_ROOT="$(cd "$(dirname "$0")" && git rev-parse --show-toplevel)"
+PROJECT="$REPO_ROOT/client"
+SCENE="res://tooling/sprite_renderer/render_scene.tscn"
+OUTPUT="$PROJECT/tooling/sprite_renderer/output"
+
+# Verify model exists
+MODEL_FILE="$PROJECT/tooling/sprite_renderer/models/${MODEL_NAME}.tscn"
+if [ ! -f "$MODEL_FILE" ]; then
+    echo "ERROR: Model not found: $MODEL_FILE"
+    echo "Available models:"
+    ls "$PROJECT/tooling/sprite_renderer/models/"*.tscn 2>/dev/null | xargs -I{} basename {} .tscn
+    exit 1
+fi
+
+echo "Rendering: $MODEL_NAME"
+echo "Godot: $GODOT"
+echo "Project: $PROJECT"
+
+# Ensure resources are imported (headless, no display needed)
+echo "Importing resources..."
+"$GODOT" --path "$PROJECT" --headless --import 2>&1 || echo "Warning: import step had errors (may be non-fatal)"
+
+# Run Godot with the render scene, passing model name as user arg
+"$GODOT" --path "$PROJECT" "$SCENE" -- "$MODEL_NAME" 2>&1
+
+# Check output
+EXPECTED_FILES=0
+for dir in north east south west; do
+    for res in 1024 256 64; do
+        f="$OUTPUT/${MODEL_NAME}_${dir}_${res}.png"
+        if [ -f "$f" ]; then
+            EXPECTED_FILES=$((EXPECTED_FILES + 1))
+        fi
+    done
+done
+
+echo ""
+echo "Generated $EXPECTED_FILES/12 files in $OUTPUT/"
+ls -la "$OUTPUT/${MODEL_NAME}"_*.png 2>/dev/null || echo "No output files found."