Set comfyui_reserve_gb default to 0.0

When ComfyUI is not running, the 10GB reservation wastes VRAM and causes
OOM errors. Default to 0, users can set AUDIOCRAFT_COMFYUI_RESERVE_GB=10
when running alongside ComfyUI.

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

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

config/settings.py

@@ -37,7 +37,7 @@ class Settings(BaseSettings):
 
     # VRAM Management
     comfyui_reserve_gb: float = Field(
-        default=10.0, description="VRAM reserved for ComfyUI (GB)"
+        default=0.0, description="VRAM reserved for ComfyUI (GB). Set via AUDIOCRAFT_COMFYUI_RESERVE_GB if running with ComfyUI."
     )
     safety_buffer_gb: float = Field(
         default=1.0, description="Safety buffer to prevent OOM (GB)"