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/src/store/themeStore.ts

@@ -0,0 +1,38 @@
+'use client'
+
+import { create } from 'zustand'
+
+export interface AccentPreset {
+  name: string
+  accent: string
+  rgb: string
+}
+
+export const ACCENT_PRESETS: AccentPreset[] = [
+  { name: 'Лайм',     accent: '#c8ff00', rgb: '200,255,0' },
+  { name: 'Синий',    accent: '#00D4FF', rgb: '0,212,255' },
+  { name: 'Розовый',  accent: '#FF2D78', rgb: '255,45,120' },
+  { name: 'Фиолет',   accent: '#A855F7', rgb: '168,85,247' },
+  { name: 'Оранж',    accent: '#FF6B35', rgb: '255,107,53' },
+  { name: 'Минт',     accent: '#00FFB2', rgb: '0,255,178' },
+]
+
+const STORAGE_KEY = 'pm_accent'
+
+interface ThemeStore {
+  accentIdx: number
+  setAccent: (idx: number) => void
+}
+
+export const useThemeStore = create<ThemeStore>((set) => ({
+  accentIdx: (() => {
+    if (typeof window === 'undefined') return 0
+    const saved = localStorage.getItem(STORAGE_KEY)
+    const idx = saved !== null ? parseInt(saved, 10) : 0
+    return idx >= 0 && idx < ACCENT_PRESETS.length ? idx : 0
+  })(),
+  setAccent: (idx) => {
+    if (typeof window !== 'undefined') localStorage.setItem(STORAGE_KEY, String(idx))
+    set({ accentIdx: idx })
+  },
+}))