feat(bal): Group C settings-dialog improvements (editable dates, narrower RAW box, warning/reset/support, tooltips, bold locktime)

C2 - 'Editable dates' option (default OFF):
  - new EDITABLE_DATES config; checkbox in settings dialog
  - WillSettingsWidget.apply_editable_dates() re-locks/unlocks the
    delivery-time and check-alive fields, called from update_all() so the
    toggle takes effect immediately (same mechanism as Hide Invalidated)
  - EDITABLE_DATES included in the Reset-to-defaults list

C3 - RAW date box narrowed to ~1/3 (input box 6 chars); the trailing
  label that shows the computed absolute date kept at 10 chars (fixed a
  truncation regression)

C4 - settings dialog:
  (a) bold red warning at the top
  (b) 'Reset setting' button restoring all 7 dialog settings to defaults
      (single source of truth: BalConfig.default), not touching wills
  (c) bold 'Support: bitcoin-after.life' link (opens via webopen)

C5 - tooltips: calendar 'Export reminder dates to your calendar (.ics)',
  fee field 'Mining fee rate in sat/vByte used for the will transactions',
  fee '丰' icon 'Miner fee, click for more information' (tooltip font scoped
  to QPushButton so it matches the other tooltips)

C6 - Locktime column rendered in bold in the will list

tests/test_group_c_settings.py: 4 new tests (EDITABLE_DATES default/toggle,
  reset restores all dialog settings incl. EDITABLE_DATES, reset leaves
  unrelated config untouched). Full suite: 210 passed.

bal/gui/qt/common.py

@@ -39,7 +39,7 @@ from electrum.gui.qt.util import (Buttons, CancelButton, ColorScheme,
                                   OkButton, TaskThread, WindowModalDialog,
                                   char_width_in_lineedit, getSaveFileName,
                                   import_meta_gui, read_QIcon_from_bytes,
-                                  read_QPixmap_from_bytes)
+                                  read_QPixmap_from_bytes, webopen)
 from electrum.i18n import _
 from electrum.logging import get_logger
 from electrum.network import BestEffortRequestFailed, Network, TxBroadcastError