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/disc.rs

@@ -691,7 +691,7 @@ impl<'a> ContentReader<'a> {
 
 fn session_read_sector(session: &mut DriveSession, lba: u32, buf: &mut [u8; 2048]) -> Result<()> {
     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, 0x00, 0x01, 0x00,
     ];