core+gui: chunked multi-QR will transfer (export/import + review/sign wizard, audio channel)

BALQR-framed chunk scheduler (bal/core/qrtransfer.py) with zlib compression,
four chunk presets and a QR_CHUNK_SIZE setting (row 16).
Export/import dialogs (WillQrExportDialog/WillQrImportDialog), per-tx
review-and-sign wizard, export filters (All/Valid/Valid-NC) and an Auto
slideshow with speed + loop for the QR codes; optional audio_modem channel
with a local receive mirror. _prepare_and_sign_tx refactor (no behaviour
change); WillItem.status defaults to '' instead of None (import crash fix);
invalidate_will guard for a missing date_to_check. Docs: PLAN_QR_TRANSFER,
QML_PLAN, README, HANDOFF, CHANGELOG entry 56, AUDIO_MODEM_DEBIAN.

README.md

@@ -26,6 +26,7 @@ bal/                     the installable Electrum plugin package
 │   ├── willexecutors.py
 │   ├── checkalive.py
 │   ├── reminders.py
+│   ├── qrtransfer.py       QR will-transfer wire format / chunk scheduler
 │   └── input_rules.py
 ├── cli/                 headless command-line layer (no Qt)
 │   ├── commands.py      bal_* daemon commands (@plugin_command)
@@ -87,6 +88,17 @@ Copy the `bal/` directory into your Electrum installation's
 `electrum/plugins/` directory, so that `electrum/plugins/bal/manifest.json`
 exists, then enable it from **Tools → Plugins**.
 
+## Transfer a will with QR codes (or audio)
+
+From the will list (**Export → QR Codes**) a will can be exported as a
+sequence of QR codes and imported on another device (**Import via QR**). The
+export offers All / Valid / Valid-NC filters plus a QR size preset
+(150–1800 bytes/frame); the import flow reviews and sign each transaction
+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.
+
 ## Command-line / headless usage
 
 BAL can be used without the Qt GUI via Electrum's daemon mode. The CLI layer