Scaffold dd0c/alert: ingestion, correlation engine, HMAC validation, tests

- Webhook ingestion: HMAC validation for Datadog/PagerDuty/OpsGenie with 5-min timestamp freshness
- Payload normalizers: canonical alert schema with severity mapping per provider
- Correlation engine: time-window grouping, late-alert attachment (2x window), FakeClock for testing
- InMemoryWindowStore for unit tests
- Tests: 12 HMAC validation cases, 5 normalizer cases, 7 correlation engine cases
- PostgreSQL schema with RLS: tenants, incidents, alerts, webhook_secrets, notification_configs
- Free tier enforcement columns (alert_count_month, reset_at)
- Fly.io config, Dockerfile, Gitea Actions CI

products/03-alert-intelligence/fly.toml

@@ -0,0 +1,27 @@
+app = "dd0c-alert"
+primary_region = "iad"
+
+[build]
+  dockerfile = "Dockerfile"
+
+[env]
+  NODE_ENV = "production"
+  PORT = "3000"
+  LOG_LEVEL = "info"
+
+[http_service]
+  internal_port = 3000
+  force_https = true
+  auto_stop_machines = true
+  auto_start_machines = true
+  min_machines_running = 0
+
+  [http_service.concurrency]
+    type = "requests"
+    hard_limit = 200
+    soft_limit = 150
+
+[[vm]]
+  cpu_kind = "shared"
+  cpus = 1
+  memory_mb = 256