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>

alembic/versions/0117_rule_moments.py

@@ -0,0 +1,38 @@
+"""rule_moments — the moments of work a rule arrives at (milestone 458 step 3)
+
+Revision ID: 0117
+Revises: 0116
+Create Date: 2026-10-05
+
+A rule mounted on a moment is delivered whenever that moment happens, by
+lookup rather than by score. The moment is a catalog name, validated by the
+service; the catalog is code, so there is no table to key it to. Cascades
+with the rule, like rule_systems beside it.
+"""
+import sqlalchemy as sa
+from alembic import op
+
+revision = "0117"
+down_revision = "0116"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "rule_moments",
+        sa.Column(
+            "rule_id", sa.BigInteger(),
+            sa.ForeignKey("rules.id", ondelete="CASCADE"), primary_key=True,
+        ),
+        sa.Column("moment", sa.Text(), primary_key=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=True),
+    )
+    # The delivery read (step 4) asks "which rules are on this moment?", the
+    # opposite direction from the primary key.
+    op.create_index("ix_rule_moments_moment", "rule_moments", ["moment"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_rule_moments_moment", table_name="rule_moments")
+    op.drop_table("rule_moments")