feat(postgres): infrastructure setup and schema creation (tasks 1-2)

- Install pg (node-postgres) dependency
- Create backend/db.js connection pool module (max 10, auto-reconnect)
- Install Docker and spin up steam-postgres container on port 5433
- Create backend/db-schema.sql with complete Postgres DDL (24 tables)
- Replace findings_json blob with ivanti_findings table (individual rows)
- Merge notes/overrides into findings table columns
- Add proper indexes: state, bu_ownership, severity, composite
- Create backend/setup-postgres.js for idempotent schema initialization
- Add DATABASE_URL to .env and .env.example
- Update migration plan docs with Docker setup commands
- Verify: schema executes cleanly, pool connects, 24 tables created

docs/guides/postgres-migration-plan.md

@@ -258,3 +258,32 @@ systemctl start cve-backend
 - **No JSON parsing**: Findings are rows, not a blob
 - **Concurrent access**: Multiple users can read while sync writes
 - **Future-proof**: Easy to add full-text search, materialized views, partitioning
+
+## Docker Container Setup
+
+Run this once to create the Postgres container:
+
+```bash
+docker run -d --name steam-postgres \
+  --restart unless-stopped \
+  -e POSTGRES_DB=cve_dashboard \
+  -e POSTGRES_USER=steam \
+  -e POSTGRES_PASSWORD=sV4xmC9xAUCFop0ypxMVS056QgPqGrX \
+  -p 5433:5432 \
+  -v steam-pgdata:/var/lib/postgresql/data \
+  postgres:16-alpine
+```
+
+Verify it's running:
+```bash
+docker ps | grep steam-postgres
+psql -h localhost -p 5433 -U steam -d cve_dashboard -c "SELECT 1;"
+```
+
+Management commands:
+```bash
+docker stop steam-postgres     # Stop
+docker start steam-postgres    # Start
+docker logs steam-postgres     # View logs
+docker exec -it steam-postgres psql -U steam -d cve_dashboard  # Shell access
+```