BAL - Bitcoin After Life Electrum plugin (v0.2.8)

Behavior-preserving refactor of the original BAL plugin with clean separation
of business logic from the PyQt GUI.

Layout:
  bal/core/   GUI-free logic (util, plugin_base, heirs, will, willexecutors)
  bal/gui/qt/ PyQt6 presentation (theme, common, widgets, calendar, dialogs,
              lists, window, plugin)
  bal/qt.py   Qt entry-point shim (works as internal and external zip plugin)
  bal/manifest.json  standard-conforming metadata

Tooling:
  build_zip.py            deterministic, zipimport-friendly archive builder
  tests/smoke_test.py     imports + behavior regression test
  tests/external_zip_test.py  reproduces Electrum's external-zip loading

Targets Electrum 4.7.2 + PyQt6. Logic kept byte-identical where possible.

bal/gui/qt/__init__.py

@@ -0,0 +1,17 @@
+"""
+bal.gui.qt
+==========
+
+The PyQt6 graphical interface of the Bitcoin After Life plugin.
+
+Module map (was previously one 4000-line ``qt.py``):
+
+    common.py    - shared imports + tiny helpers (shown_cv, add_widget, ...)
+    theme.py     - colour mapping for will-item statuses (was WillItem.get_color)
+    calendar.py  - .ics calendar generation
+    widgets.py   - reusable leaf widgets (editors, checkboxes, will box, ...)
+    dialogs.py   - all dialogs (settings, wizard, build-will, detail, ...)
+    lists.py     - tree views (heirs, preview, will-executors)
+    window.py    - BalWindow controller (one per wallet window)
+    plugin.py    - Plugin class with the Electrum @hook methods (entry point)
+"""