Add new accent colours and replace legacy ones

[ajuncosa]

Resolves: #33863

Related to: musescore/MuseScore#33974

[coderabbitai]

📝 Walkthrough

Walkthrough

UiConfiguration::possibleAccentColors() now returns updated hardcoded accent color lists. The dark-mode list is expanded to more hex values, and the light-mode list is replaced with new values. The function still selects the dark list in dark mode and the light list otherwise.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	⚠️ Warning	The PR description only links the issue and related PR, but it omits the required summary, motivation, and checklist from the template.	Add a short change summary and motivation, then complete the required checklist items in the repository template.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: replacing legacy accent colours with new ones.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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