introduce Clarity a high-contrast, large lyrics font theme

[dgruss]

This PR adds Clarity, an accessibility-focused theme built around high contrast, low visual noise, and strong readability. The theme uses a mostly white-on-dark presentation with restrained blue accents, making menus, lyrics, player information, and score elements easier to scan in dim rooms, on TVs, and from longer viewing distances.

Theme Goals

• Improve readability with large, high-contrast text.
• Prefer clean dark panels over busy or decorative backgrounds.
• Keep interaction states visible without relying on subtle color shifts.
• Make lyrics and core gameplay information the visual priority.
• Provide a calmer alternative to more image-heavy or colorful themes.

Notes

Clarity is based on the existing Modern theme structure, but simplifies the visual treatment and emphasizes accessible contrast.

Screenshots