Correct retirement docs: deactivation clears future open instances

Retirement preserves the definition row, schedule rule, assignees,
windows and all durable completion history, but like any deactivation
it regenerates, so future uncompleted instances are cleared and none
are recreated while inactive. Fixes the "deletes nothing / all
instances preserved" wording in the core docstrings, the admin DELETE
route description, ADMIN-SPEC and the retire test's docstring
(review finding NQ-262-1). No behavioural change.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_quest_definitions.py

@@ -2212,9 +2212,10 @@ def test_delete_without_history_keeps_a_shared_rule(tmp_path) -> None:
 def test_delete_with_history_retires_and_preserves_everything(
     tmp_path,
 ) -> None:
-    """A completion event on ANY instance: nothing is deleted; the
-    definition is deactivated and its row, rule, assignees, windows,
-    instance and completion history all remain."""
+    """A completion event on ANY instance: the definition is retired
+    (deactivated) and its row, rule, assignees, windows and completion
+    history all remain.  The completed instance survives; only future
+    UNCOMPLETED instances are cleared by the deactivation's regeneration."""
     async def _body(database, children, rules, definitions, child):
         created = await create_quest_definition(
             database, "Brush teeth", _daily_rule(), [child.id], ["morning"]