feat(bal): Group A (timestamps + statuses + anticipate docs) and Group B (auto-sign) v0.3.4

Bump plugin version to 0.3.4 (manifest, __init__, plugin_base, VERSION).

GROUP A
- A1: remove block-height locktimes; the plugin now uses UNIX timestamps
  only. The NLOCKTIME_BLOCKHEIGHT_MAX guard is kept on purpose (it forces
  every locktime to be a timestamp). chk_locktime is now 2-arg; int_locktime
  and anticipate_locktime no longer accept blocks; RAW input only accepts d/y.
  Two now-dormant configs (LOCKTIME_BLOCKS, LOCKTIMEDELTA_BLOCKS) are kept with
  comments to avoid touching persisted keys.
- A2: rename PENDING -> MEMPOOL everywhere (label 'Mempool', yellow #ffce30);
  add new UPDATED status; ANTICIPATED & UPDATED keep VALID; documented
  set_status rules; backward-compat migration (old PENDING -> MEMPOOL).
- A3: clarify that anticipating to a future date only rebuilds (never
  invalidates), while only a past locktime invalidates (WillExpired). Code was
  already correct; only the comment and docs were fixed.

Colour follow-up: UPDATED lightened from #800080 to #b266b2 (more readable),
updated in theme.py, docs and the theme test.

GROUP B
- B1: verified the 'Create your will' button already opens the guided wizard
  (no code change needed).
- B2: new persisted AUTO_SIGN setting (default ON) with an 'Auto-sign on Check'
  checkbox in the settings dialog. When enabled, Check signs and broadcasts
  automatically; the wallet password is requested only for encrypted wallets.

B2 follow-up (fixes reported after testing):
- Remove the duplicate sign/broadcast cycle in lists.check(); build_will_task()
  already signs and broadcasts.
- Suppress the manual 'press Sign/Broadcast' hint and its popup when AUTO_SIGN
  is ON (kept when OFF).
- Make broadcast one-shot: removed the retry flag and the Exception('retry');
  failed will-executors stay PUSH_FAIL and are skipped (no endless retry).
  PUSHED transactions are already excluded from re-collection.

Docs: inheritance-options.md/.html and inheritance-flow.svg updated to v0.3.4.
Tests: 206 passing (new test_anticipate_manual_locktime, test_anticipate_past_locktime,
test_group_b_auto_sign; updated core/util, core/will_extra, gui/theme, gui/widgets).
CHANGELOG.md added with one numbered entry per task.

bal/gui/qt/theme.py

@@ -22,8 +22,9 @@ status into a colour for the transaction list / detail views.
 _STATUS_COLOR_PRIORITY = (
     ("INVALIDATED", "#f87838"),  # orange  - tx can no longer be mined
     ("REPLACED", "#ff97e9"),     # pink    - superseded by another tx
+    ("UPDATED", "#b266b2"),      # light violet - replaced keeping same locktime+heirs
     ("CONFIRMED", "#bfbfbf"),    # grey    - already mined
-    ("PENDING", "#ffce30"),      # yellow  - in mempool, waiting
+    ("MEMPOOL", "#ffce30"),      # yellow  - seen in the Electrum mempool
 )
 
 # Default colour used when no status in the priority list matches.