feat: add Pivoine custom ComfyUI nodes for DiffRhythm

Add custom node wrapper PivoineDiffRhythmRun that fixes tensor dimension
mismatch error by disabling chunked VAE decoding. The original DiffRhythm
node's overlap=32 parameter conflicts with the VAE's 64-channel architecture.

Changes:
- Add comfyui/nodes/pivoine_diffrhythm.py: Custom node wrapper
- Add comfyui/nodes/__init__.py: Package initialization
- Add arty.yml setup/pivoine-nodes: Deployment script for symlink
- Update all 4 DiffRhythm workflows to use PivoineDiffRhythmRun

Technical details:
- Inherits from DiffRhythmRun to avoid upstream patching
- Forces chunked=False in diffrhythmgen() override
- Requires more VRAM (~12-16GB) but RTX 4090 has 24GB
- Category: 🌸Pivoine/Audio for easy identification

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

arty.yml

@@ -368,6 +368,34 @@ scripts:
       exit 1
     fi
 
+  setup/pivoine-nodes: |
+    echo "========================================="
+    echo "  Linking Pivoine Custom Nodes"
+    echo "========================================="
+    echo ""
+
+    NODES_SRC="/workspace/ai/comfyui/nodes"
+    NODES_DEST="/workspace/ComfyUI/custom_nodes/ComfyUI_Pivoine"
+
+    # Remove existing symlink if present
+    if [ -L "$NODES_DEST" ] || [ -d "$NODES_DEST" ]; then
+      echo "Removing existing: $NODES_DEST"
+      rm -rf "$NODES_DEST"
+    fi
+
+    # Create symlink
+    ln -s "$NODES_SRC" "$NODES_DEST"
+
+    echo ""
+    echo "✓ Pivoine custom nodes linked"
+    echo "  Source: $NODES_SRC"
+    echo "  Linked: $NODES_DEST"
+    echo ""
+    echo "Available Pivoine nodes:"
+    echo "  🌸 PivoineDiffRhythmRun - DiffRhythm with chunked disabled"
+    echo ""
+    echo "Category: 🌸Pivoine/Audio"
+
   setup/comfyui-extensions-deps: |
     echo "========================================="
     echo "  Installing ComfyUI Extensions Dependencies"