feat(v0.4.7): report area 500px, heirs one-per-line, wizard line breaks, ALL-DUST guard

Owner-approved changes after testing v0.4.6, plus accumulated v0.4.x work,
task-tracking notes, and an updated project HANDOFF document.

The four v0.4.7 changes:

1. Report area (BalBuildWillDialog) opens 500px tall (min) up to 700px (max),
   then the scrollbar takes over. Previously it opened ~140px (too short).

2. Heirs are listed ONE per line again (green, bold) in _build_success_report,
   reverting the v0.4.6 single-line form. Heir names can be long and the report
   now scrolls, so compression is no longer needed.

3. Two wizard texts get an explicit line break: after "(or backup)" in the date
   hint and after "miner fees" in the fee note (widgets.py).

4. ALL-DUST guard: when EVERY heir's share is below the Bitcoin dust limit, the
   inheritance would pay nobody. Heirs.prepare_lists now raises
   HeirAmountIsDustException at the end (where all heirs across all locktimes
   are known with their final dust state), and dialogs.task_phase1 shows a clear
   RED message and stops without building/signing/checking. A mix of dust +
   valid heirs keeps building normally. The guard is intentionally in
   prepare_lists, NOT prepare_transactions (which only sees the lowest locktime
   and would false-positive). HeirAmountIsDustException is imported in common.py.

Tests: 3 new tests in test_core_heirs_extra.py pin the dust behaviour (all-dust
raises; mixed continues; multi-locktime continues). Full suite: 258 passed.
ruff: no new errors. Version bumped 0.4.6 -> 0.4.7 (4 files). CHANGELOG #23.

Also adds/updates HANDOFF.md so any future AI (Claude or another model) can
resume the project with full context (rules, layout, build/test/lint, dust
logic, git flow), and records the task-tracking notes in
.agent_memory_tasks.md.

tests/test_group_g_basic_calendar.py

@@ -0,0 +1,79 @@
+"""
+Tests for the BASIC-mode calendar reminders.
+
+Context: in BASIC mode the check-alive parameter is hidden and not managed by
+the user, so calendar reminders cannot be spread over the check-alive period as
+they are in ADVANCED mode. Instead the calendar uses three fixed reminders -
+30, 10 and 1 day before the inheritance delivery date - and drops any reminder
+that would fall in the past.
+
+These tests pin the behaviour of the pure helper ``basic_reminder_offsets`` that
+drives that decision.
+
+``basic_reminder_offsets`` lives in ``bal.gui.qt.widgets`` (which imports
+PyQt6), so these tests are run headless with ``QT_QPA_PLATFORM=offscreen`` like
+the other GUI tests.
+
+Run:
+    QT_QPA_PLATFORM=offscreen PYTHONPATH=electrum-src \
+        python3 -m pytest tests/test_group_g_basic_calendar.py -q
+"""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), os.pardir))
+
+from bal.gui.qt.widgets import (BASIC_REMINDER_OFFSETS,
+                                 basic_reminder_offsets)
+
+
+def test_basic_offsets_all_future():
+    """A far delivery date keeps all three fixed reminders (30, 10, 1)."""
+    assert basic_reminder_offsets(365) == [30, 10, 1]
+
+
+def test_basic_offsets_exactly_30_days():
+    """Exactly 30 days away: the 30-day reminder is still valid (<=)."""
+    assert basic_reminder_offsets(30) == [30, 10, 1]
+
+
+def test_basic_offsets_drops_30_when_too_close():
+    """20 days away: the 30-day reminder is in the past and is dropped."""
+    assert basic_reminder_offsets(20) == [10, 1]
+
+
+def test_basic_offsets_only_one_left():
+    """5 days away: only the 1-day reminder remains."""
+    assert basic_reminder_offsets(5) == [1]
+
+
+def test_basic_offsets_empty_when_deadline_today():
+    """Delivery date less than a day away: no reminder fits."""
+    assert basic_reminder_offsets(0) == []
+
+
+def test_basic_offsets_empty_when_negative():
+    """A past delivery date (negative days) yields no reminders."""
+    assert basic_reminder_offsets(-10) == []
+
+
+def test_basic_offsets_are_a_subset_of_the_fixed_set():
+    """Whatever the horizon, results are always a subset of the fixed offsets."""
+    for horizon in (-1, 0, 1, 9, 10, 11, 29, 30, 100):
+        result = basic_reminder_offsets(horizon)
+        assert set(result).issubset(set(BASIC_REMINDER_OFFSETS))
+        # Always sorted descending (earliest reminder first) and every offset >= 1.
+        assert result == sorted(result, reverse=True)
+        assert all(off >= 1 for off in result)
+
+
+if __name__ == "__main__":
+    test_basic_offsets_all_future()
+    test_basic_offsets_exactly_30_days()
+    test_basic_offsets_drops_30_when_too_close()
+    test_basic_offsets_only_one_left()
+    test_basic_offsets_empty_when_deadline_today()
+    test_basic_offsets_empty_when_negative()
+    test_basic_offsets_are_a_subset_of_the_fixed_set()
+    print("all BASIC calendar reminder tests passed")