Improve PDF generation with proper A4 sizing and borders

- Move PDF border size to settings.py
- Use standard A4 dimensions (210x297mm)
- Fix aspect ratio preservation in layout function
- Use img2pdf's built-in layout function with proper border specification

pdf_cleaner.py

@@ -20,6 +20,7 @@ class Settings:
     TRIM_PADDING_PIXELS = 20
     MONOCHROME_THRESHOLD = 127
     OPTIPNG_OPTIMIZATION_LEVEL = 7
+    PDF_BORDER_SIZE = 50
 
 settings = Settings()
 
@@ -379,9 +380,21 @@ def finalize(output_pdf):
     
     print(f"Combining {len(temp_files)} pages into {output_pdf}...")
     
-    # Convert to PDF
+    # A4 size in millimeters
+    A4_WIDTH_MM = 210
+    A4_HEIGHT_MM = 297
+    
+    # Convert to PDF with border
     with open(output_pdf, "wb") as f:
-        f.write(img2pdf.convert(temp_files))
+        f.write(img2pdf.convert(
+            temp_files,
+            with_pdfrw=True,
+            layout_fun=img2pdf.get_layout_fun(
+                pagesize=(img2pdf.mm_to_pt(A4_WIDTH_MM), img2pdf.mm_to_pt(A4_HEIGHT_MM)),
+                border=(settings.PDF_BORDER_SIZE,) * 4,  # Same border size for all sides (top, right, bottom, left)
+                fit=img2pdf.FitMode.into
+            )
+        ))
     
     # Clean up temporary files
     print("Cleaning up temporary files...")