P1: Monitoring Module — Cloud Monitoring + Alerting Terraform

Add Terraform module for Cloud Monitoring dashboards, uptime checks, and alert policies for the 4 Rosetta services. Components: 1. Uptime checks — HTTP health probe for gateway, ship, shop, shield (every 60s) 2. Alert policies: - Service down (uptime check fails 2 consecutive) → PagerDuty/email - Error rate >5% over 5 min → warning - Latency p95 >5s → warning - Cloud SQL CPU >80% → warning - Pub/Sub dead letter messages >0 → critical 3. Dashboard: - Request rate per service - Latency distribution (p50, p95, p99) - Error rate - Cloud SQL connections + CPU - Pub/Sub message throughput - Revenue metering (calls/hour from c8_usage_records) Output: c8-infra/terraform/modules/monitoring/main.tf Target: c8-infra/terraform/modules/monitoring/