Initial commit: LibreDrive unlocker plugin for libfreemkv

New crate freemkv-unlock-ld — the LibreDrive Unlocker implementation,
split out of libfreemkv so the library stays firmware-clean on crates.io.

Owns everything about HOW MediaTek MT1959 drives are firmware-unlocked:
  - profiles.json (the bundled drive-profile database + DriveProfile parse)
  - src/platform/mt1959/* (variant-A/B firmware upload + unlock handshake)
  - WRITE_BUFFER / MODE SELECT upload, unlock CDBs, disc-speed calibration

Exposes LibreDrive::new() implementing libfreemkv::Unlocker (name/matches/
unlock). Plug it in with one line at process start:

  libfreemkv::register_unlocker(Box::new(freemkv_unlock_ld::LibreDrive::new()));

Depends on libfreemkv (path-patched via gitignored .cargo/config.toml in
dev) for the trait, ScsiTransport, DriveId, and Result. README notes it's
the LibreDrive unlocker (attribution to be added by owner).

README.md

@@ -0,0 +1,23 @@
+# freemkv-unlock-ld
+
+The **LibreDrive** unlocker plugin for [libfreemkv](https://github.com/freemkv/libfreemkv).
+
+libfreemkv ships only the `Unlocker` trait + registry and stays firmware-clean.
+This crate owns *how* MediaTek MT1959 drives are firmware-unlocked: the bundled
+drive-profile database (`profiles.json`), the firmware blobs, the
+WRITE_BUFFER / MODE SELECT upload, the unlock CDBs, and the variant-A / variant-B
+handshake logic.
+
+## Usage
+
+Register the unlocker once at process start, before any rip:
+
+```rust
+libfreemkv::register_unlocker(Box::new(freemkv_unlock_ld::LibreDrive::new()));
+```
+
+That single line is the whole plug. Any drive whose identity matches a bundled
+profile is firmware-unlocked at drive-prep; everything else falls through to
+libfreemkv's host-certificate AACS handshake.
+
+<!-- TODO(owner): add MakeMKV / LibreDrive attribution. -->