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_tiff_convert.rs

@@ -0,0 +1,33 @@
+use telfax::document::pdf::{pdf_to_fax_document, tiff_to_fax_document};
+use telfax::config::FaxResolution;
+use std::path::Path;
+
+fn main() {
+    let tiff_path = "/Users/accusys/telfax/test/testfax.tif";
+    let tiff_data = std::fs::read(tiff_path).expect("Failed to read TIFF");
+
+    println!("=== Testing TIFF → FaxDocument conversion ===");
+    println!("Input TIFF: {} bytes", tiff_data.len());
+
+    let doc = tiff_to_fax_document(&tiff_data).expect("Conversion failed");
+
+    println!("Converted successfully:");
+    println!("  Pages: {}", doc.pages.len());
+    for (i, page) in doc.pages.iter().enumerate() {
+        println!("  Page {}: {}x{} pixels, {} bytes",
+            i + 1, page.width_pels, page.rows, page.pixels.len());
+    }
+
+    // Verify pixel data - check some sample values
+    let page = &doc.pages[0];
+    let bytes_per_row = ((page.width_pels + 7) / 8) as usize;
+    
+    println!("  Bytes per row: {}", bytes_per_row);
+    println!("  Expected rows: {}", page.rows);
+    println!("  Actual data rows: {}", page.pixels.len() / bytes_per_row);
+
+    // Sample first few bytes of first row
+    println!("  First row bytes (hex): {:02x?}", &page.pixels[0..8.min(bytes_per_row)]);
+    
+    println!("\n=== Test Passed ===");
+}