feat: redesigned dashboard UI with editorial aesthetic and RTL support

- Replace Dashboard/Comparison with DashboardDemo/PeriodSelectorDemo as primary pages at / and /comparison
- New editorial design: DM Serif Display + Outfit fonts, inline period picker, multi-select filters for museum/channel/district
- Full Arabic RTL support with IBM Plex Sans Arabic; EN/AR toggle synced to global LanguageContext
- Bar/pie chart toggle + absolute/percent toggle for museum, channel, district charts
- Refined top nav: transparent inactive links, accent active state, visual separator between nav links and utilities
- DateRangePicker, MultiSelect, FilterControls shared components added
- NavDemo: sidebar layout alternative (accessible at /nav-demo)

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

src/components/Login.tsx

@@ -53,7 +53,9 @@ function Login({ onLogin }: LoginProps) {
         <p className="login-subtitle">{t('login.subtitle')}</p>
 
         <form onSubmit={handleSubmit}>
+          <label htmlFor="pin-input" className="sr-only">{t('login.placeholder')}</label>
           <input
+            id="pin-input"
             type="password"
             inputMode="numeric"
             value={pin}