disc: credit firmware unlock in the bus-encryption gate

The bus-key gate only credited the cert handshake's read_data_key as proof
bus encryption was removed. A firmware unlocker removes it AT THE DRIVE
(serves clear content) and yields no read_data_key — so a SUCCESSFUL
firmware unlock (VID present, read_data_key None) tripped the gate and
blocked ALL key resolution, including the online source. That was the
root cause of live UHD discs reporting "missing keys" after an unlock.

Now a single predicate answers "is bus encryption gone?": never-had-it ||
file/ISO || firmware-unlocked || cert-bus-key. The gate is just
`if !bus_encryption_removed { error }` — no enumerated cases. HandshakeResult
gains `drive_unlocked`, and the read_data_key failure reason is captured so
the warn says WHY the bus key is missing.

Also: reword the first hardware-sense escalation as "fast-fail escalation"
(it is often transient — the drive recovers), reserving "wedge" for a
persistent run; and scrub the product name from core comments (it belongs
only in the unlocker crate).

src/drive/mod.rs

@@ -393,7 +393,7 @@ impl Drive {
     /// Initialize drive — unlock + firmware upload.
     /// Optional. Adds features: removes riplock, enables UHD reads, speed control.
     ///
-    /// The LibreDrive/OEM firmware unlock is required for BD/UHD (AACS) reads,
+    /// The firmware/OEM unlock is required for BD/UHD (AACS) reads,
     /// but it puts the drive in an extended-access state where stock CSS
     /// authentication no longer works — so a CSS-protected DVD can't be read.
     /// For a DVD we therefore SKIP the unlock and run the drive in its normal
@@ -1245,7 +1245,7 @@ mod command_tests {
 
     /// `disc_is_dvd()` must match the DVD profile family (0x0010..=0x001F)
     /// and ONLY that family. A false positive on a BD/UHD profile (0x0040+)
-    /// would skip the LibreDrive firmware unlock that UHD reads require; a
+    /// would skip the firmware unlock that UHD reads require; a
     /// false negative on a DVD would re-introduce the CSS read failure. The
     /// Current Profile is bytes 6-7 of the GET CONFIGURATION header.
     /// Mutation: widening the range to `..=0x0040` makes the BD-ROM assert