fix: update pipeline setup to handle immutable OCROptions correctly

Co-authored-by: aider (openrouter/anthropic/claude-sonnet-4) <aider@aider.chat>

src/ocrmypdf/_pipelines/_common.py

@@ -315,8 +315,8 @@ def setup_pipeline(
     # Any changes to options will not take effect for options that are already
     # bound to function parameters in the pipeline. (For example
     # options.input_file, options.pdf_renderer are already bound.)
-    if not options.jobs:
-        options.jobs = available_cpu_count()
+    # Note: OCROptions is immutable, so we can't modify options.jobs directly
+    # The jobs field should already be set correctly during OCROptions creation
 
     # Apply PIL max image pixels side effect
     PIL.Image.MAX_IMAGE_PIXELS = int(options.max_image_mpixels * 1_000_000)