feat(disc): read CD-DA off a real drive, measured before it was written

New crate `qbz-disc`: table of contents and raw audio sectors through the
kernel's own cdrom ioctls. No libcdio — not because libcdio is worse (it is
better at RIPPING than this will ever be) but because this path PLAYS a clean
disc, and for that the kernel interface is enough while a native library would
have to be built into Flatpak, Snap and AppImage. Both need the same --device
permission in a sandbox; only one needs the library shipped.

Every claim below was measured on the owner's USB drive with Tool — Fear
Inoculum BEFORE a line of this crate existed, so the design answers evidence
rather than the other way round:

  - the TOC reads back 7 audio tracks, lead-out at LSN 356568, and the track
    lengths match the record exactly (10:21, 11:52, 12:44, 13:37, 10:05, 4:48,
    15:44 — 79:11 total);
  - CDROMREADAUDIO over 20 frames from LSN 4000 returned 47 040 bytes, 99 %
    non-zero samples, peak 14559: real audio, not silence;
  - the drive hands back LITTLE-endian samples. Neighbouring-sample deltas
    average 73.5 read as LE against 20 971 read as BE, a 285x margin, so the
    bytes go straight into a little-endian WAV with no swap. That is one
    drive, so `looks_byte_swapped` keeps the test available as a diagnostic
    instead of an article of faith;
  - the disc's MCN is all zeros, which is why identity is a digest over the
    track table and not the catalogue number.

What this is NOT is accurate extraction: no overlap synchronisation, no cache
modelling, no jitter verification. On a clean disc that is fine for playback,
and an unreadable sector surfaces as an ERROR rather than a hole full of
zeros — silence that pretends to be audio is the one outcome a bit-perfect
player must never produce.

`/dev/sr0` is nowhere in the code: drives are enumerated, because a box can
have several and /dev/cdrom is a symlink that may point at any of them. Data
tracks of a mixed-mode disc are skipped by their control bits.

`CdRef` is the typed reference (`cdda:/dev/sr0#285735+70833`) with ONE parser,
not prefix tests copied around — the scattered version is a known failure mode
here and cost a whole session on 2026-08-20.

11 tests, several asserting against that real table of contents.

cc

crates/qbz-disc/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "qbz-disc"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]
+log = { workspace = true }
+thiserror = { workspace = true }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+libc = "0.2"