redesign: Phantom/Backpack vibe — Syne + DM Sans + clean dark UI

Replace all-mono JetBrains font stack with Syne (headings) + DM Sans
(body) + JetBrains Mono (data/numbers only). Remove cursor:crosshair,
scanlines overlay, and grid background pattern. New palette: #0D0B14
bg, #13111C cards, Solana mint/purple accents. Rounded cards, cleaner
typography hierarchy, better readability throughout.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 0xeeli