feat: add selectable routing groups and composite billing

Support per-model provider enablement and compact model editing. Capture request-time billing factors, charge customer costs separately, and preserve historical statistics without backfills.

crates/aether-data/runtime/src/backend/stats/postgres_daily/mod.rs

@@ -159,6 +159,12 @@ async fn perform_stats_aggregation_for_day(
         .execute(&mut *tx)
         .await?;
 
+    sqlx::query(UPDATE_STATS_DAILY_BILLING_COST_SQL)
+        .bind(day_start_utc)
+        .bind(day_end_utc)
+        .execute(&mut *tx)
+        .await?;
+
     let model_rows =
         upsert_stats_daily_model_rows(&mut tx, day_start_utc, day_end_utc, now_utc).await?;
     let provider_rows =

crates/aether-data/runtime/src/backend/stats/postgres_daily/sql.rs

@@ -2404,6 +2404,18 @@ WHERE created_at >= $1
   AND provider_name NOT IN ('unknown', 'pending')
 "#;
 
+// Keep customer consumption separate from the upstream procurement-cost rollup.
+pub(super) const UPDATE_STATS_DAILY_BILLING_COST_SQL: &str = r#"
+UPDATE stats_daily SET billing_cost=(
+  SELECT round(COALESCE(sum(billable_amount),0),8)
+  FROM usage_analytics_facts_v1
+  WHERE created_at >= $1 AND created_at < $2
+    AND status NOT IN ('pending','streaming')
+    AND provider_name NOT IN ('unknown','pending')
+)
+WHERE date=$1
+"#;
+
 #[cfg(test)]
 mod tests {
     use super::{