Theme selection screen

[anarchyysm]

Problem

Goal: user can switch themes directly on the device without editing files.
Estimated effort: 1–2 days

Proposed Solution

• Implement folder listing of themes/ in the screens/display_settings/ screen
• Implement color preview for the listed theme (display main tokens without applying them)
• Implement selection and confirmation: save theme name to config/screen.conf
• Implement live reapplication of global lv_style_t without requiring a reboot
• Test: switch from default to matrix on the device — screens change immediately
• Test: insert a custom theme copied to SD — it appears in the list normally

Use Case

No response

Alternatives Considered

No response