docs: QR/audio will transfer notes

README.md

@@ -26,7 +26,8 @@ bal/                     the installable Electrum plugin package
 │   ├── willexecutors.py
 │   ├── checkalive.py
 │   ├── reminders.py
-│   ├── qrtransfer.py       QR will-transfer wire format / chunk scheduler
+│   ├── qrtransfer.py       BAL QR will-transfer wire format / chunk scheduler
+│   ├── animated_qr.py      BC-UR v1/v2 + BBQR codecs (stdlib-only)
 │   └── input_rules.py
 ├── cli/                 headless command-line layer (no Qt)
 │   ├── commands.py      bal_* daemon commands (@plugin_command)
@@ -97,7 +98,19 @@ export offers All / Valid / Valid-NC filters plus a QR size preset
 one at a time, then proposes exporting the signed transactions. When
 Electrum's `audio_modem` plugin is enabled (optional, requires `amodem` +
 PortAudio) Send/Receive audio buttons complement the QR channel. See
-[`PLAN_QR_TRANSFER.md`](PLAN_QR_TRANSFER.md) for the full wire-format spec.
+[`PLAN_QR_TRANSFER.md`](PLAN_QR_TRANSFER.md) for the BAL QR wire-format spec.
+
+### Animated-QR formats (interop)
+
+BAL QR is the default export format, but the export page's **Format** selector
+also emits **BC-UR v1** (`ur:bytes`, BC32 + SHA-256), **BC-UR v2**
+(`ur:bytes`, CBOR fountain codes) and **BBQR** (`B$…`, Coinkite, used by
+BitKit) animated-QR sequences. The importer auto-detects the format of each
+code it sees, so any of the four formats can be imported on a BAL device, and
+a BAL export can be imported by any tool that understands these standards.
+UR v2 imports tolerate out-of-order and duplicate frames (fountain decoding);
+BBQR frames may arrive in any order. Rotation/redundancy caps and the
+32 MB message limit (zlib-bomb guard) bound untrusted scanner input.
 
 ## Command-line / headless usage