feat(client): id helper + leaf canon-log entities with owned invariants

Also configure GUT to not treat push_error() as a test failure
(client/.gutconfig.json: failure_error_types = [engine, gut]).
The brief's LogPlayer/Quest setters intentionally push_error() on
rejected input; GUT's default failure_error_types includes
push_error, which would fail test_player_rejects_unknown_class and
test_quest_status_enum despite their assertions passing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/.gutconfig.json

@@ -2,5 +2,6 @@
   "dirs": ["res://tests/unit"],
   "include_subdirs": true,
   "log_level": 1,
-  "should_exit": true
+  "should_exit": true,
+  "failure_error_types": ["engine", "gut"]
 }