lint: ruff cleanup pass across bal/ and tests/

- Sort imports and fix pyproject ruff config (per-file ignores for
  intentional Qt/core exceptions)
- Mark Heirs.validate_* helpers as @staticmethod
- Clean up dead code, rename shadowing vars, use raise ... from
- Add AGENTS.md with env/lint/test/release guidance

tests/test_core_heirs_extra.py

@@ -8,19 +8,20 @@ Run:
     QT_QPA_PLATFORM=offscreen python3 tests/test_core_heirs_extra.py
 """
 
-import sys
 import os
+import sys
 from unittest.mock import MagicMock, patch
 
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), os.pardir))
 
 from bal.core.heirs import (
-    Heirs, create_op_return_script, reduce_outputs,
-    HEIR_ADDRESS, HEIR_AMOUNT, HEIR_LOCKTIME, HEIR_REAL_AMOUNT,
+    HEIR_AMOUNT,
+    Heirs,
+    create_op_return_script,
+    reduce_outputs,
 )
 from bal.core.willexecutors import Willexecutors
 
-
 # ------------------------------------------------------------------ #
 # Heirs db-dependent methods
 # ------------------------------------------------------------------ #
@@ -188,7 +189,7 @@ def test_validate_address_invalid():
         from bal.core.heirs import NotAnAddress
         try:
             Heirs.validate_address("bad")
-            assert False, "should have raised"
+            raise AssertionError("should have raised")
         except NotAnAddress:
             pass