Refactor AdminSettings into modular components

Split 1123-line monolithic AdminSettings.tsx into 11 modules:

Components:
- icons.tsx (85 lines) - All SVG icons
- Toggle.tsx (21 lines) - Reusable toggle component
- SettingInput.tsx (89 lines) - Text/select input for settings
- SettingRow.tsx (104 lines) - Single setting card
- BrandingTab.tsx (212 lines) - Logo, name, animation settings
- ThemeTab.tsx (277 lines) - Theme presets and custom colors
- FavoritesTab.tsx (59 lines) - Starred settings display
- SettingsTab.tsx (144 lines) - Accordion categories view

Utilities:
- constants.ts (55 lines) - MENU_SECTIONS, THEME_PRESETS
- utils.ts (35 lines) - formatSettingKey, stripHtml
- index.ts (13 lines) - Barrel exports

Result: AdminSettings.tsx reduced from 1123 to 251 lines

src/components/admin/Toggle.tsx

@@ -0,0 +1,21 @@
+interface ToggleProps {
+  checked: boolean
+  onChange: () => void
+  disabled?: boolean
+}
+
+export function Toggle({ checked, onChange, disabled }: ToggleProps) {
+  return (
+    <button
+      onClick={onChange}
+      disabled={disabled}
+      className={`relative w-12 h-6 rounded-full transition-colors ${
+        checked ? 'bg-accent-500' : 'bg-dark-600'
+      } ${disabled ? 'opacity-50 cursor-not-allowed' : 'cursor-pointer'}`}
+    >
+      <div className={`absolute top-1 w-4 h-4 bg-white rounded-full transition-transform ${
+        checked ? 'left-7' : 'left-1'
+      }`} />
+    </button>
+  )
+}