Improves entity tree and message detail UX - #173

Enhances the entity browsing experience and message detail view:

• Entity Tree & Navigation:

  • Implements an entity filter that now intelligently searches within topic subscriptions, automatically expanding topics that contain matching subscriptions.
  • Introduces a dedicated "Entity Selection Footer" that displays comprehensive metadata for the currently selected queue, topic, or subscription, and centralizes contextual actions in a single, accessible flyout.
  • Moves inline action buttons (e.g., create, details, delete) for subscriptions from directly within the entity tree items to the new selection footer, significantly decluttering the tree view.
  • Refactors entity tree styling and templates to provide clearer visual indicators for item selection and expansion, improving overall readability and interaction.
  • Updates topic selection logic to consistently load subscriptions and toggle the expansion state when a topic name is clicked.

• Message Details & Actions:

  • Redesigns the message detail dialog into a modern, slide-out drawer, offering a more fluid and less intrusive user experience.
  • Adds a direct delete capability for individual messages from within the message detail drawer, streamlining message management.
  • Refines the presentation of message metadata within the drawer, organizing less frequently accessed information into an expandable section.
  • Enhances accessibility for the message detail drawer, including improved focus management and support for closing the drawer with the Escape key.