feat(hub): usage fact ledger for run-scoped cost attribution (ADR-0026) (#4)

Co-authored-by: Hong Jiarong <me@jrhim.com>
Co-committed-by: Hong Jiarong <me@jrhim.com>

hub/test/unit/feishu-reactions.test.ts

@@ -290,6 +290,9 @@ function mockPrisma(): PrismaClient {
       findUnique: vi.fn(async () => null),
       update: vi.fn(async () => ({ id: "run-1" })),
     },
+    usageFact: {
+      create: vi.fn(async () => ({ id: "fact-1" })),
+    },
     projectAgentLock: {
       findUnique: vi.fn(async () => (lock === null ? null : { runId: lock.runId })),
       create: vi.fn(async (args: { data: { projectId: string; runId: string } }) => {