Migrate runtime and local stack from S3 to GCS

[joyzoursky]

Summary

• Migrate object storage integration from S3/MinIO to GCS for runtime artifacts and files.
• Switch the local Docker stack from MinIO to fake-gcs-server and bootstrap bucket creation.
• Update operator and deployment docs to use GCS configuration.

Changes

• Replace S3 config keys with GCS keys in app config and .env.example.
• Replace S3ObjectStore with GcsObjectStore, including emulator-mode operations and signed URL generation.
• Remove AWS S3 SDK dependencies and add @google-cloud/storage.
• Update local infra targets/services (make services-*, infra/docker/docker-compose.local.yml) to run GCS emulator and bucket bootstrap.
• Refresh README/operator/helm docs to reference GCS variables and workflows.

Validation

• Lint: npm run verify (pass)
• Tests: Not run separately (verify covers lint + TypeScript compile + audit)
• Manual: Not run in this session
• Audit: npm audit --audit-level=moderate --package-lock-only pass (5 low-severity advisories only)

Breaking Changes

• Storage environment variables changed from S3_* to GCS_* (GCS_BUCKET, GCS_PROJECT_ID, optional GCS_SERVICE_ACCOUNT_JSON_BASE64, optional STORAGE_EMULATOR_HOST for local emulator).
• Local object-storage endpoint changed from MinIO (9000/9001) to fake-gcs-server (4443).

Risks

• Storage access will fail if environments are not updated with the new GCS variables.
• Any scripts/runbooks still referencing MinIO/S3 variable names may break until updated.

Follow-ups

• Remove remaining low-severity audit advisories in the GCS dependency chain when a compatible upgrade path is available.
• Confirm staging/production secret rotation from S3 keys to GCS settings is complete.