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

src/document/pdf.rs

@@ -0,0 +1,98 @@
+use crate::error::{FaxError, Result};
+use crate::document::convert::{DocumentFormat, FaxDocument, Page};
+use crate::config::FaxResolution;
+use std::path::Path;
+use std::process::Command;
+
+/// Convert PDF to FaxDocument using Ghostscript.
+pub fn pdf_to_fax_document(pdf_path: &Path, resolution: FaxResolution) -> Result<FaxDocument> {
+    let dpi_arg = match resolution {
+        FaxResolution::Standard => "204x98",
+        FaxResolution::Fine => "204x196",
+        FaxResolution::SuperFine => "204x392",
+    };
+
+    let tiff_path = pdf_path.with_extension("fax.tif");
+    tracing::info!("Converting PDF {} to TIFF {}", pdf_path.display(), tiff_path.display());
+
+    let output = Command::new("gs")
+        .arg("-dBATCH")
+        .arg("-dNOPAUSE")
+        .arg("-q")
+        .arg("-sDEVICE=tiffgray")
+        .arg(format!("-r{}", dpi_arg))
+        .arg(format!("-sOutputFile={}", tiff_path.display()))
+        .arg(pdf_path)
+        .output()
+        .map_err(|e| FaxError::document(format!("Failed to run ghostscript: {}", e)))?;
+
+    tracing::info!("Ghostscript exit status: {:?}", output.status);
+    if !output.status.success() {
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        let stdout = String::from_utf8_lossy(&output.stdout);
+        tracing::error!("Ghostscript stderr: {}", stderr);
+        tracing::error!("Ghostscript stdout: {}", stdout);
+        return Err(FaxError::document(format!(
+            "Ghostscript failed: exit code {:?}",
+            output.status.code()
+        )));
+    }
+
+    let tiff_data = std::fs::read(&tiff_path)?;
+    let doc = tiff_to_fax_document(&tiff_data)?;
+
+    std::fs::remove_file(&tiff_path).ok();
+
+    Ok(doc)
+}
+
+/// Read TIFF-F and convert to FaxDocument with 1-bit pixel data.
+pub fn tiff_to_fax_document(tiff_data: &[u8]) -> Result<FaxDocument> {
+    use tiff::decoder::Decoder;
+    use std::io::Cursor;
+
+    let mut cursor = Cursor::new(tiff_data);
+    let mut decoder = Decoder::new(&mut cursor)
+        .map_err(|e| FaxError::document(format!("Failed to open TIFF: {}", e)))?;
+
+    let (width, height) = decoder.dimensions()
+        .map_err(|e| FaxError::document(format!("Failed to get TIFF dimensions: {}", e)))?;
+
+    let bytes_per_row = ((width + 7) / 8) as usize;
+    let mut pixels = vec![0u8; bytes_per_row * height as usize];
+
+    let mut result = decoder.read_image()
+        .map_err(|e| FaxError::document(format!("Failed to read TIFF image: {}", e)))?;
+
+    // Convert to 1-bit packed format
+    let buffer = result.as_buffer(0);
+    let img_data = buffer.as_bytes();
+
+    // Process each pixel - TIFF is grayscale (8-bit), convert to 1-bit
+    for (i, &byte) in img_data.iter().enumerate() {
+        let pixel_idx = i % width as usize;
+        let row_idx = i / width as usize;
+        let byte_idx = pixel_idx / 8;
+        let bit_idx = 7 - (pixel_idx % 8);
+
+        // WhiteIsZero: 0=white, 255=black
+        // We want: 1=black, 0=white (MSB first)
+        if byte < 128 {
+            let idx = row_idx * bytes_per_row + byte_idx;
+            if idx < pixels.len() {
+                pixels[idx] |= 1 << bit_idx;
+            }
+        }
+    }
+
+    let page = Page {
+        pixels,
+        width_pels: width,
+        rows: height,
+    };
+
+    Ok(FaxDocument {
+        pages: vec![page],
+        format: DocumentFormat::Tiff,
+    })
+}