fix: always pass outscale explicitly to ensure correct upscaling

The outscale parameter was set to None when scale == netscale,
which caused unexpected downscaling behavior. Now explicitly pass
the user's selected scale to ensure correct 2x or 4x output.

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

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

src/processing/upscaler.py

@@ -214,7 +214,10 @@ def upscale_image(
     # Determine output scale
     if scale is None:
         scale = model_info.scale
-    outscale = scale / model_info.netscale if scale != model_info.netscale else None
+
+    # Always pass outscale explicitly to ensure correct output size
+    # The outscale parameter directly controls the final output scale factor
+    outscale = scale
 
     # Process
     if progress_callback: