feat(workers): schedule billing reconciliation workers alongside other jobs

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Closes #1214

Summary

Adds BILLING_RECON_INTERVAL_MS, BILLING_RECON_BATCH_SIZE, and BILLING_RECON_GRACE_PERIOD_MS configuration in src/config/env.ts and src/config/index.ts, adds createPostgresReconciliationStore and batchSize/gracePeriodMs options in src/services/billingReconciliationJob.ts, and wires billingReconJob into src/index.ts startup (startServer), graceful shutdown (shutdownSubsystems), and resource cleanup (closeAllDataResources).

Acceptance Criteria Mapping

• BillingReconciliationJob is started when the server boots and stopped during graceful shutdown: Registered in shutdownSubsystems, closeAllDataResources, and startServer in src/index.ts.
• Reconciliation runs are persisted to reconciliation_runs via a Postgres store: Implemented createPostgresReconciliationStore(db) in src/services/billingReconciliationJob.ts.
• Interval, batch size, and grace period are configurable via environment variables with sensible defaults: Added BILLING_RECON_INTERVAL_MS, BILLING_RECON_BATCH_SIZE, and BILLING_RECON_GRACE_PERIOD_MS.
• Unit tests cover the scheduled lifecycle and graceful drain: Verified in src/services/billingReconciliationJob.test.ts.

Validation

• npx jest src/services/billingReconciliationJob.test.ts --no-cache (all 13 tests pass).

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Payout Wallet (Base Mainnet USDC / EVM): 0x3806cd592a508d1992Ed007C2F53de251C2E7452