Add PDF to fax conversion support

- pdf.rs: Ghostscript-based PDF to TIFF-F conversion
- tiff_to_fax_document: Parse TIFF and convert to 1-bit fax format
- CLI: Add 'convert' subcommand for dry testing
- CLI: Add resolution option for send command
- Test files for PDF/TIFF conversion validation

test/test_conversion.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+import subprocess
+import os
+
+# Test PDF to TIFF-F conversion
+pdf_path = "/Users/accusys/telfax/test/testfax.pdf"
+tiff_path = "/Users/accusys/telfax/test/testfax_converted.tif"
+
+print("=== Testing PDF → TIFF-F Conversion ===")
+
+# Run ghostscript
+result = subprocess.run([
+    "gs", "-dBATCH", "-dNOPAUSE", "-q",
+    "-sDEVICE=tiffg3",
+    "-r204x196",  # Fine resolution
+    "-sOutputFile", tiff_path,
+    pdf_path
+], capture_output=True, text=True)
+
+if result.returncode != 0:
+    print(f"Ghostscript failed: {result.stderr}")
+    exit(1)
+
+# Check output
+if os.path.exists(tiff_path):
+    size = os.path.getsize(tiff_path)
+    print(f"✓ TIFF-F created: {tiff_path}")
+    print(f"  Size: {size} bytes")
+    
+    # Get TIFF info
+    import struct
+    
+    with open(tiff_path, 'rb') as f:
+        header = f.read(8)
+        if header[:2] == b'II':
+            print("  Byte order: Little-endian")
+        elif header[:2] == b'MM':
+            print("  Byte order: Big-endian")
+        
+        # Read IFD offset
+        if header[:2] == b'II':
+            ifd_offset = struct.unpack('<I', header[4:8])[0]
+        else:
+            ifd_offset = struct.unpack('>I', header[4:8])[0]
+        
+        f.seek(ifd_offset)
+        num_entries = struct.unpack('<H' if header[:2] == b'II' else '>H', f.read(2))[0]
+        print(f"  IFD entries: {num_entries}")
+        
+        # Read key tags
+        for i in range(num_entries):
+            tag = struct.unpack('<H' if header[:2] == b'II' else '>H', f.read(2))[0]
+            type_ = struct.unpack('<H' if header[:2] == b'II' else '>H', f.read(2))[0]
+            count = struct.unpack('<I' if header[:2] == b'II' else '>I', f.read(4))[0]
+            value_offset = f.read(4)
+            
+            # Tags of interest: 256=width, 257=height, 259=compression, 262=photometric
+            if tag == 256:  # Width
+                val = struct.unpack('<I' if header[:2] == b'II' else '>I', value_offset)[0]
+                print(f"  Width: {val} pixels")
+            elif tag == 257:  # Height
+                val = struct.unpack('<I' if header[:2] == b'II' else '>I', value_offset)[0]
+                print(f"  Height: {val} lines")
+            elif tag == 259:  # Compression
+                val = struct.unpack('<H' if header[:2] == b'II' else '>H', value_offset[:2])[0]
+                comp_names = {1: "None", 3: "Group 3 MH", 4: "Group 4 MMR"}
+                print(f"  Compression: {comp_names.get(val, val)}")
+            elif tag == 262:  # PhotometricInterpretation
+                val = struct.unpack('<H' if header[:2] == b'II' else '>H', value_offset[:2])[0]
+                photo_names = {0: "WhiteIsZero", 1: "BlackIsZero"}
+                print(f"  Photometric: {photo_names.get(val, val)}")
+else:
+    print("✗ TIFF-F not created")
+    exit(1)
+
+print("\n=== Conversion Test Passed ===")