core+gui: BBQR-only QR transfer, disable Audio when modem plugin unavailable

- Drop BALQR / BC-UR v1 / v2 wire formats, keep BBQR only (animated_qr,
  qrtransfer, dialogs); remove the settings "QR Code Size" selector and
  persist the export-dialog size choice instead.
- Disable the Audio transport radio button in the import/export dialogs
  when the audio_modem plugin (or its amodem dependency) is unavailable.
- Refresh translation catalogs (bal.pot, es_ES, it_IT).

bal/core/plugin_base.py

@@ -305,11 +305,10 @@ class BalPlugin(BasePlugin):
         # stay display-only outside the wizard unless the user opts in.
         self.EDITABLE_DATES = BalConfig(config, "bal_editable_dates", False)
 
-        # QR_CHUNK_SIZE (will transfer via QR): payload budget, in bytes, used
-        # per QR frame when exporting/importing a will through the QR channel.
-        # The settings dialog offers the 4 standard presets of
-        # bal.core.qrtransfer.CHUNK_PRESETS; this stores the selected budget.
-        # Default 150 (small QR, low-resolution cameras).
+        # QR_CHUNK_SIZE (will transfer via QR): payload budget, in characters,
+        # used per QR frame when exporting/importing a will through the QR
+        # channel. The export dialog seeds its own size selector from this
+        # value (default 150, small QR, low-resolution cameras).
         self.QR_CHUNK_SIZE = BalConfig(config, "bal_qr_chunk_size", 150)
 
         # NUM_REMINDERS (Group D / D1): how many SEPARATE reminder events the