feat: runtime accent color picker with 6 presets

Replace all hardcoded #c8ff00 / rgba(200,255,0,...) with CSS custom
properties (--accent, --accent-rgb) so the accent color updates live.
Add themeStore (Zustand + localStorage) with 6 presets (Лайм, Синий,
Розовый, Фиолет, Оранж, Минт). Add ThemeApplier component that syncs
CSS vars on load. Add color picker UI section in ExtraTab.

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

apps/web/tailwind.config.ts

@@ -8,7 +8,9 @@ const config: Config = {
         bg: '#0a0a0f',
         surface: '#12121a',
         surface2: '#1a1a26',
-        accent: '#c8ff00',
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        accent: (({ opacityValue }: { opacityValue?: string }) =>
+          opacityValue !== undefined ? `rgba(var(--accent-rgb),${opacityValue})` : 'var(--accent)') as any,
         muted: '#555555',
         'app-text': '#f0f0f0',
       },