V1.0: Class 1 fax — real-world 4-page send to external number confirmed

Core features:
- Class 1 T.30 protocol: full send/receive implementation
- HDLC: DLE-stuffing, FCS strip, USR5637 bit-reversal handling
- T.4 MH encoder/decoder (1728px A4 standard)
- Document pipeline: PDF (Ghostscript), PNG, TIFF input
- Width clamping: US Letter 1734px → 1728px fax standard
- Cover page: CJK rasterization (TW/CN/JP/EN), TIFF + HTML output
- OCR verification: Tesseract 5 with eng+chi_tra, CJK space-tolerant
- API server (axum): health, send, jobs, cover, retry, cancel
- Background worker: auto-poll queue, speed fallback, retry policy
- Modem detection, pool management

Real-world test results (2026-07-23):
- V90 → 25153038: 4 pages, V.17 12000 bps, 2:33 ✅
- USR5637 → 25153038: 4 pages, V.17 12000 bps, 2:26 ✅
- Both faxes confirmed received on remote machine

Tested: loopback (100% pixel match), multi-page, all input formats,
cover pages, OCR verify, API endpoints, worker processing.
13 unit tests pass, 0 new clippy warnings.

examples/modem_test.rs

@@ -0,0 +1,43 @@
+use std::io::{Read, Write};
+use std::time::Duration;
+
+fn main() {
+    let mut port = serialport::new("/dev/cu.usbmodem00000021", 115200)
+        .data_bits(serialport::DataBits::Eight)
+        .flow_control(serialport::FlowControl::None)
+        .parity(serialport::Parity::None)
+        .stop_bits(serialport::StopBits::One)
+        .timeout(Duration::from_millis(5000))
+        .open()
+        .expect("Failed to open");
+
+    port.write_all(b"AT\r").unwrap();
+    port.flush().unwrap();
+    std::thread::sleep(Duration::from_millis(500));
+    
+    let mut buf = vec![0u8; 1024];
+    match port.read(&mut buf) {
+        Ok(n) => println!("AT response: {:?}", String::from_utf8_lossy(&buf[..n])),
+        Err(e) => println!("Error: {}", e),
+    }
+
+    port.write_all(b"AT+FTH=?\r").unwrap();
+    port.flush().unwrap();
+    std::thread::sleep(Duration::from_millis(1000));
+    
+    let mut buf = vec![0u8; 1024];
+    match port.read(&mut buf) {
+        Ok(n) => println!("AT+FTH=? response: {:?}", String::from_utf8_lossy(&buf[..n])),
+        Err(e) => println!("Error: {}", e),
+    }
+
+    port.write_all(b"AT+FTM=?\r").unwrap();
+    port.flush().unwrap();
+    std::thread::sleep(Duration::from_millis(1000));
+    
+    let mut buf = vec![0u8; 1024];
+    match port.read(&mut buf) {
+        Ok(n) => println!("AT+FTM=? response: {:?}", String::from_utf8_lossy(&buf[..n])),
+        Err(e) => println!("Error: {}", e),
+    }
+}