[WIP] Add UI tests implementation for demo video

[Copilot]

Implementation Plan for Independent UI Tests

• Create test suite directory structure (e2e tests)
• Set up Playwright test configuration for independent tests
• Extract and implement individual test cases from demo scenarios:
  • Connection test (connect to MQTT broker)
  • Numeric plots test (chart visualization)
  • JSON preview test (formatted messages)
  • Diff capability test (message changes)
  • Clipboard operations test (copy topic/value)
  • Tree search/filter test
  • SparkplugB decoding test
  • Settings menu test
  • Advanced connection settings test
  • Keyboard shortcuts test
• Make tests independent and deterministic
• Add test utilities and helpers
• Create new GitHub workflow job for parallel test execution
• Update package.json scripts to run new test suite
• Add documentation for running tests
• Verify all tests pass independently

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement tests</issue_title>
<issue_description>Thre is a demo video n which many features are tested and visualized, this includes currently all UI tests.

• Identify test cases
• Create a separate suite to test theses cases
• Tests should be independent of each other
• Tests should be deterministic
• apply best practices for testing web based UIs
• run tests in a separate job, parallel to the demo video</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement tests #917

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