feat(ui): support lcov coverage reporter

[nami8824]

Description

Previously, the UI coverage viewer only supported the html reporter. This PR adds support for the lcov reporter,
which generates coverage reports in lcov-report/index.html.

Note: When both reporters are configured, html takes priority for backward compatibility.

Resolves #6381

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Tests

• Run the tests with pnpm test:ci.

Documentation

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Changesets

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