Build Basic Observer GUI and Subscription Management

[Dumdart]

Summary

Introduce the foundational Smart Home Observer GUI, including workspace navigation, MQTT connection status, subscription management, topic details, and log display.

Changes

Bug Fixes

• Improve MQTT callbacks, repository updates, and observer message processing.
• Refine connection and subscription state handling.

Features

• Add the main GUI window, view model, and reusable interface components.
• Add subscription creation and settings workflows.
• Add observer tree, topic details, connection status, and log console views.
• Integrate GUI startup through the application entry point.

Refactoring

• Extend core observer, connection-status, and subscription models.
• Organize MQTT gateway, client, repository, and callback interactions for GUI support.

Improvements

• Update project configuration and expand automated coverage for GUI, MQTT, repository, processing, and subscription behavior.

Testing

• Updated unit tests covering GUI behavior, view-model state, MQTT client interactions, observer processing, repository operations, and subscriptions.