test(e2e): add encryption e2e tests for per-project encryption

Covers:
- Admin encrypt/decrypt endpoints (enable/disable, idempotency checks)
- Encrypted artifact upload + download round trip
- Presigned URL suppression for encrypted projects
- Encrypted message store + retrieve
- Batch encrypt existing unencrypted data
- Batch decrypt to disable encryption
- Key rotation with DEK re-wrap
- Encryption metadata validation (no admin DEK)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: GenerQAQ