feat(billing): activate real-time quota enforcement pipeline

- Wire relay handler to increment_usage() for JSON responses (tokens + relay_requests)
- Wire relay handler to increment_dimension("relay_requests") for SSE streams
- Add increment_dimension() function for hand_executions/pipeline_runs dimensions
- Schedule AggregateUsageWorker hourly for reconciliation (run_on_start=true)
- Mount mock payment routes in dev mode (ZCLAW_SAAS_DEV=true)

Previously the quota middleware always allowed requests because usage
counters were never incremented. Now relay requests update billing_usage_quotas
in real-time, with the aggregator providing hourly reconciliation.

config/saas-development.toml

@@ -31,4 +31,5 @@ jobs = [
   { name = "cleanup_rate_limit", interval = "5m", task = "cleanup_rate_limit", run_on_start = false },
   { name = "cleanup_refresh_tokens", interval = "1h", task = "cleanup_refresh_tokens", run_on_start = false },
   { name = "cleanup_devices", interval = "24h", task = "cleanup_devices", run_on_start = false },
+  { name = "aggregate_usage", interval = "1h", task = "aggregate_usage", run_on_start = true, args = { account_id = null } },
 ]