feat: add agent cost reporting

hub/prisma/schema.prisma

@@ -247,6 +247,10 @@ model AgentRun {
   summary           String?
   inputTokens       Int?
   outputTokens      Int?
+  /// Provider/gateway-reported cost in USD. Null means this run has no trusted cost fact.
+  costUsd           Decimal?       @db.Decimal(18, 8)
+  /// Semantic source of costUsd, e.g. provider_reported. Not a pricing-estimate fallback.
+  costSource        String?
   metadata          Json
   error             String?
   startedAt         DateTime       @default(now())
@@ -261,6 +265,7 @@ model AgentRun {
   fileChanges AgentFileChange[]  @relation("runFileChanges")
 
   @@index([projectId, status])
+  @@index([projectId, finishedAt])
   @@index([sessionId])
   @@index([requestedByUserId])
   @@index([updatedAt])