feat(database): enable Data API and connection logging

[konokenj]

Issue

close #122

Problem

The Aurora Serverless v2 cluster lacks operational tooling for debugging and diagnostics:

• No Data API: Operators must use SSH tunneling via Bastion Host to run ad-hoc SQL queries, which is cumbersome during incident response.
• No connection logging: Diagnosing unexpected auto-pause resumes or connection pool exhaustion requires guesswork, as PostgreSQL connection events are not recorded.

Solution

Add three CDK-native properties to the existing DatabaseCluster construct:

1. enableDataApi: true — Enables the RDS Data API, allowing direct SQL execution from AWS CLI/Console without SSH tunneling.
2. log_connections / log_disconnections — Standard PostgreSQL parameters that record connection open/close events in the PostgreSQL log.
3. cloudwatchLogsExports: ["postgresql"] with 1-week retention — Exports PostgreSQL logs to CloudWatch Logs for centralized analysis (Aurora PostgreSQL CloudWatch Publishing).

Changes

• cdk/lib/constructs/database.ts:
  • Added import * as logs from "aws-cdk-lib/aws-logs"
  • Added enableDataApi: true to DatabaseCluster
  • Added cloudwatchLogsExports: ["postgresql"] and cloudwatchLogsRetention: logs.RetentionDays.ONE_WEEK
  • Added log_connections: "1" and log_disconnections: "1" to the existing ParameterGroup

Verification

• npm run build passes in cdk/
• After deployment:
  • aws rds-data execute-statement can run SQL against the cluster
  • CloudWatch log group /aws/rds/cluster/<cluster-name>/postgresql is created
  • Connection/disconnection events appear in the log stream