TestRunner: add --skip-screenshots option to accelerate local UI test

[tzi]

Description

This PR introduces a new UI test runner flag: --skip-screenshots.

When enabled, UI tests still execute normally (fixtures, navigation, interactions, API calls, waits, JS/runtime checks), but screenshot diff assertions are skipped.

Why this is valuable

• Screenshot comparison is often unreliable locally because rendering depends on OS-level differences (for example, font rendering).
• Makes local debugging faster when visual diffs are not the focus, or when investigating logic/regression issues.
• Unblocks development in environments missing image tooling.

How it looks

Checklist

• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules

Review

• Functional review done
• Potential edge cases thought about (behaviour of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• New documentation added or existing documentation updated

[sgiehl]

@tzi Nice idea. But actually the screenshot in the PR and how it really looks does not macht. There is no info message that screenshots are skipped when that happens, the tests just silently turn green.

[tzi]

@tzi Nice idea. But actually the screenshot in the PR and how it really looks does not macht. There is no info message that screenshots are skipped when that happens, the tests just silently turn green.

Thanks for the feedback.
It's interesting, because I use it a lot since I created it. I will check if I forgot something in this PR.

[tzi]

@sgiehl Yes, I've forgot to add the console.log() is this PR. It's updated now