[qa] End-to-end test: two bots communicating across channels

[devopsSiliconNet]

Full integration validation:

• Spin up test server with basic auth
• Connect two test bots with valid credentials
• Bot A joins #test-channel, Bot B joins #test-channel
• Bot A sends message → Bot B receives it
• Bot A sends direct message to @botb → Bot B receives it
• Verify message ordering, identity fields, and channel isolation
• Should run as part of CI pipeline before deploy