feat(moments): rules mount on moments, through every rule door (milestone 458 step 3, #4921)

rule_moments (migration 0117) records which moments a rule arrives at, by
catalog name, cascading with the rule. rule_detail, the one seam every
rule door already returns through, gains moments beside system_ids: None
leaves the mounts alone, a list replaces them. get_rule and both
list_rules doors read them back, batched per page.

All five MCP rule/preference writes and the three REST ones take moments
and validate them before their create or update. An unknown name is
refused with the catalog listed and leaves no half-made rule behind; a
parity test pins that ordering on every door.

Backup v22 carries the mounts as a join table remapped through the rule
map; a real-Postgres round trip checks they land on the restored rule.

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

src/scribe/models/__init__.py

@@ -78,7 +78,7 @@ from scribe.models.user_profile import UserProfile  # noqa: E402, F401
 # Imported before rulebook: rule_systems foreign-keys canonical_systems.
 from scribe.models.canonical_system import CanonicalSystem  # noqa: E402, F401
 from scribe.models.rulebook import (  # noqa: E402, F401
-    Rulebook, RulebookTopic, Rule, RuleRelation, rule_systems,
+    Rulebook, RulebookTopic, Rule, RuleRelation, rule_moments, rule_systems,
 )
 # After notes and rules: it foreign-keys both (milestone 440).
 from scribe.models.lesson_rule_link import LessonNoRule, LessonRuleLink  # noqa: E402, F401