Add multicolor gradient to mic ring, buttons, and toggles

[phillsatellite]

Summary

• Mic button idle ring — slowly rotating conic gradient (indigo → violet → pink) using CSS @property animation. Stops and snaps to solid red when recording.
• New chat button — gradient background replacing the previous flat surface style
• API key submit button — gradient background
• Settings toggles (on state) — gradient background replacing flat accent color

Gradient palette: #6366f1 (indigo) → #a855f7 (violet) → #ec4899 (pink)

Test plan

• Idle mic ring shows rotating gradient border
• Mic ring switches to solid red when recording
• New chat button shows gradient
• API key submit button shows gradient
• Settings → Formats toggles show gradient when enabled
• Settings → Account dark mode toggle shows gradient when on