Custom RGB profiles — save and switch lighting presets

[karava]

Problem

Users want to save multiple RGB lighting configurations and switch between them (e.g. gaming profile, typing profile, dark mode).

Upstream ref: the-via/app#115 (3👍)

Desired behavior

• Save named RGB profiles (effect, color, speed, brightness)
• Quick-switch between profiles
• Optionally bind profiles to layers
• Import/export profiles