feat(4636): rule pull-through per surface, and per-rule usage with confirmed lessons on list_rules

retrieval_telemetry gains rule_usage.by_source, the twin of usage.by_source:
distinct rules each surface showed, how many an agent opened, and a ratio
that is null on a bulk delivery. list_rules(with_usage=True, days=N) adds
each rule's usage, windowed, and how many lessons are confirmed instances
of it, so linked and unlinked rules can be compared through MCP.

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

tests/test_services_rule_usage.py

@@ -198,6 +198,47 @@ async def test_usage_for_rules_aggregates_per_rule(_dispose_engine):
             await s.commit()
 
 
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_usage_for_rules_counts_only_the_window_it_is_given(_dispose_engine):
+    """Two windows have to be comparable, so an event before `since` is left
+    out of every count — and without `since` it is counted."""
+    from datetime import datetime, timedelta, timezone
+
+    from sqlalchemy import delete
+
+    from grimoire.models import async_session
+    from grimoire.models.rule_usage import RuleUsageEvent
+
+    old = datetime.now(timezone.utc) - timedelta(days=30)
+    async with async_session() as s:
+        s.add_all([
+            RuleUsageEvent(user_id=990022, rule_id=6011, event=SURFACED,
+                           source="write_path_rule", created_at=old),
+            RuleUsageEvent(user_id=990022, rule_id=6011, event=PULLED,
+                           source="mcp_get_rule", created_at=old),
+            RuleUsageEvent(user_id=990022, rule_id=6011, event=SURFACED,
+                           source="write_path_rule"),
+        ])
+        await s.commit()
+    try:
+        since = datetime.now(timezone.utc) - timedelta(days=14)
+        recent = (await rule_usage.usage_for_rules([6011], since=since))[6011]
+        assert recent["surfaced_count"] == 1
+        assert recent["pull_count"] == 0
+        assert recent["last_pulled_at"] is None
+
+        everything = (await rule_usage.usage_for_rules([6011]))[6011]
+        assert everything["surfaced_count"] == 2
+        assert everything["pull_count"] == 1
+    finally:
+        async with async_session() as s:
+            await s.execute(
+                delete(RuleUsageEvent).where(RuleUsageEvent.user_id == 990022)
+            )
+            await s.commit()
+
+
 @pytest.mark.integration
 @pytest.mark.asyncio
 async def test_usage_for_rules_on_an_empty_id_list_asks_the_database_nothing(