core+gui: compact BAL QR v2 wire format + best-of compression default

BAL QR export now ships a fixed 11-char 'BAL1<TTT><iii><F><payload>' header
(3-char base36 zero-padded count fields, cap 46655 frames) and, by default,
the shorter of plain vs zlib+base64 (flag '0'/'Z'). parse_frame remains dual:
legacy 'BALQR1|total|index|flags|' frames still import. detect_format accepts
'BAL1'. New exports are not readable by builds older than this change.

Also add a will-detail test for heir/willexecutor addresses and decoded
OP_RETURN payloads. Docs updated (CHANGELOG, COMPATIBILITY, PLAN_QR_TRANSFER,
README); 345 core tests + 89 GUI tests pass.

bal/gui/qt/dialogs.py

@@ -53,6 +53,7 @@ from ...core.qrtransfer import (
     QrTransferError,
     decode_transfer,
     encode_transfer,
+    encode_transfer_best,
     preset_index_for_chunk_size,
     split_frames,
 )
@@ -2799,6 +2800,12 @@ class BalQrExportWidget(QWidget):
         self.tx_strings = list(tx_strings)
         self._stop_auto()
         self.transfer = encode_transfer(self.tx_strings, compress=False)
+        # BAL QR now ships compact (best-of) compressed by default: smaller
+        # frames, and the importer reverses it via the per-frame flag. The
+        # other formats keep the raw transfer (they compress internally).
+        self._balqr_transfer, self._balqr_compressed = encode_transfer_best(
+            self.tx_strings
+        )
         self._refresh_frames()
         self._update_intro()
         self._render()
@@ -2810,7 +2817,9 @@ class BalQrExportWidget(QWidget):
     def _refresh_frames(self):
         if self.format == "balqr":
             self.frames = split_frames(
-                self.transfer, self.chunk_size, compressed=False
+                self._balqr_transfer,
+                self.chunk_size,
+                compressed=self._balqr_compressed,
             )
         else:
             self.frames = encode_animated_frames(