feat: Add separate env files for blog and wallet deployments

- Support --blog-env and --wallet-env options in deploy-swarm.sh
- Create .env.blog.example and .env.wallet.example with documented settings
- Update docker-compose.yml to use BLOG_ENV_FILE and WALLET_ENV_FILE
- Add missing REACT_APP_APP_SESSION_TIME to testing env files
  - Blog: 64800 (18 hours, posting key)
  - Wallet: 900 (15 minutes, active key)

The session time difference is critical for security: wallet uses the
active key which requires shorter sessions than blog's posting key.