Named constants, error codes, SCSI opcodes, flow documentation

- Error codes as public constants (E_DEVICE_NOT_FOUND etc.) — single source of truth
- SCSI opcodes as named constants (SCSI_READ_10, SCSI_REPORT_KEY, etc.)
- AACS key class constant, MKB format constant
- No magic numbers in CDB construction
- docs/disc-to-rip.md — end-to-end flow from disc insert to decrypted content
- Links all module docs together as a starting point

src/drive.rs

@@ -133,7 +133,7 @@ impl DriveSession {
     /// Standard SCSI READ(10) for disc filesystem data (UDF, MPLS, CLPI).
     pub fn read_disc(&mut self, lba: u32, count: u16, buf: &mut [u8]) -> Result<usize> {
         let cdb = [
-            0x28, 0x00,
+            crate::scsi::SCSI_READ_10, 0x00,
             (lba >> 24) as u8, (lba >> 16) as u8, (lba >> 8) as u8, lba as u8,
             0x00,
             (count >> 8) as u8, count as u8,