Record serving subscription provider accounts

[mylukin]

Summary

• record the concrete subscription provider account that served each request in decision telemetry
• preserve per-attempt provider metadata for request detail debugging
• surface provider and subscription account fields in request list/detail/admin decision chain UI

Tests

• corepack pnpm test
• corepack pnpm typecheck
• corepack pnpm lint
• corepack pnpm build
• git diff --check