Fix August lock not appearing in HomeKit due to invisible error messages

[Copilot]

This PR fixes a critical issue where August Smart Lock Pro + Gen 3 devices are detected by the plugin but don't appear in HomeKit, leaving users confused with no visible error messages.

Problem

When August locks have homeKitEnabled: true (common for Pro models), they won't be registered with Homebridge unless the user explicitly sets overrideHomeKitEnabled: true in their configuration. However, the error message explaining this requirement was only logged at debug level (debugErrorLog), making it invisible to most users who don't have debug logging enabled.

Users would see:

[August] Total August Locks Found: 1

But no locks would appear in HomeKit, with no indication of why.

Solution

1. Improved error visibility: Changed debugErrorLog to errorLog for homeKitEnabled devices without override, making the error visible to all users regardless of logging level.

2. Clearer error message: Replaced the technical error message with a user-friendly one:

   Device: [Lock Name] already has HomeKit enabled. To register with Homebridge, add "overrideHomeKitEnabled": true to your device config.
   

3. Better general error handling: Changed generic device registration failures from debugErrorLog to warnLog for improved visibility.

4. Comprehensive testing: Added 4 new test cases covering all registerDevice scenarios to prevent regressions.

5. Documentation: Added a troubleshooting section to the README with clear configuration examples.

Impact

Users will now immediately see why their August lock isn't appearing in HomeKit and know exactly how to fix it. No more silent failures or hunting through debug logs to understand configuration issues.

Fixes #178.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.