12. Task: Add connector configuration and diagnostics tests

[smithaldon1]

Parent Epic

#206

Purpose

Add the test coverage needed to keep connection management safe and reviewable.

Acceptance Criteria

• Unit tests cover connection schema validation and redacted serialization.
• API tests cover profile CRUD, test connection, error states, and secret redaction.
• Adapter tests use fake OPC-UA, MQTT, and BACnet clients.
• UI tests cover Connections, Protocol Diagnostics, and tag/source browser states.
• Playwright covers creating a disabled/test profile and viewing diagnostics.

Implementation Order

Step 12. Add focused tests with each slice, then complete this card as the cross-feature coverage pass.

Test Plan

Run relevant backend, frontend, and Playwright commands documented in docs/TESTING.md.