Fix message panel widget showing icon in loading state

[JvnSlv]

Overview

Closes: #153

Fix icon being presented in loading state.
Adds golden test for MessagePanelWidget

Checklist

Implementation

• Implementation matches ticket acceptance criteria and technical notes
• Manually tested against Acceptance Criteria
• UI checked in Light / Dark mode

Stability

• Checked if changes affect any features and verified affected features work as expected
• Added unit tests for new code and verified existing tests work as expected

Code quality

• Updated CHANGELOG.md, README.md and package versions in pubspec.yaml
• Dependencies are updated to latest versions or new tickets are created if there are breaking changes or deprecations
• If an unrelated part of the codebase needs to be updated or refactored, create tickets with proposed changes