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

src/scribe/models/rulebook.py

@@ -188,6 +188,21 @@ rule_systems = Table(
 )
 
 
+# Which MOMENTS of work a rule arrives at (milestone 458). A rule mounted on a
+# moment is delivered whenever that moment happens, by lookup and with no
+# score — the route for a rule that is about WHEN something is done rather
+# than what it is about, which semantic retrieval structurally misses. The
+# moment is a catalog NAME (`services/moments.py`), not a key: the catalog is
+# code, so there is nothing to point a foreign key at, and the service refuses
+# an unknown name before it is stored.
+rule_moments = Table(
+    "rule_moments",
+    Base.metadata,
+    Column("rule_id", BigInteger, ForeignKey("rules.id", ondelete="CASCADE"), primary_key=True),
+    Column("moment", Text, primary_key=True),
+    Column("created_at", DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)),
+)
+
 class RuleRelation(Base, CreatedAtMixin):
     """A typed edge between two rules. Each kind exists because its ABSENCE
     forced a workaround somewhere in the operator's rulebook (note 3026).