Add EHSAN favicon and localized browser tab titles (Task #21)

The browser tab previously showed a generic placeholder favicon and the
English title "EHSAN Closed Donation Loop". Per the reference, the tab now
shows the EHSAN logo mark and an Arabic platform title.

Changes:
- Favicon: copied the existing EHSAN logo (src/assets/ehsan-logo.png) to
  public/favicon.png and pointed index.html at %BASE_URL%favicon.png
  (base-path safe; verified it serves 200 image/png).
- Static head: index.html <title> and OG/Twitter titles + description now
  use the Arabic platform name "منصة إحسان".
- Per-page titles: added a DocumentTitle component
  (src/hooks/useDocumentTitle.ts) rendered in the Router that sets
  document.title to "<page name> - <platform>" based on the current wouter
  path and active language, reading from a new translations.meta section
  (AR + EN). Home reads "الصفحة الرئيسية - منصة إحسان"; switches with language.

Approach note: titles are centralized in the router rather than edited into
each page file, keeping it DRY while covering all main routes.

Verified: tsc clean; e2e confirmed titles on /, /opportunities, /cart and
English fallback ("Home - EHSAN Platform"), plus favicon load.

artifacts/ehsan-poc/src/App.tsx

@@ -6,6 +6,7 @@ import { LanguageProvider } from "./contexts/LanguageContext";
 import { CartProvider } from "./contexts/CartContext";
 import { AuthProvider, useAuth } from "./contexts/AuthContext";
 import { AppLayout } from "./components/layout/AppLayout";
+import { DocumentTitle } from "./hooks/useDocumentTitle";
 import NotFound from "@/pages/not-found";
 import { ComponentType } from "react";
 
@@ -37,6 +38,7 @@ function Protected({ component: Component }: { component: ComponentType<any> })
 function Router() {
   return (
     <AppLayout>
+      <DocumentTitle />
       <Switch>
         <Route path="/" component={Home} />
         <Route path="/about/:section?" component={About} />