Add About EHSAN dropdown nav + About page

Task #15: Make «عن إحسان» top-nav a real dropdown and build the About page.

- Header.tsx: converted static «عن إحسان» span into a dropdown trigger
  replicating the existing services dropdown pattern (aboutOpen state,
  trigger/panel refs, outside-click + Escape handling). Desktop panel and
  mobile nav both list «من نحن» (/about) and «اللجان» (/about/committees).
- New pages/about.tsx: green intro panel («نبذة عن إحسان») + tab strip
  (الرؤية والرسالة / الأهداف والركائز / المزايا والمجالات) for the Who-we-are
  view, and a committee card grid for the Committees view. Section chosen via
  /about/:section? route param; in-page toggle between the two. Reuses Reveal
  for scroll-in.
- App.tsx: registered <Route path="/about/:section?" component={About} />.
- translations.ts: added full bilingual `about` section (AR + EN).

Fully bilingual via existing t.* system, RTL verified, no emojis.
tsc passes; screenshots confirm both views render correctly.

artifacts/ehsan-poc/src/App.tsx

@@ -10,6 +10,7 @@ import { ComponentType } from "react";
 
 // Page imports
 import Home from "./pages/home";
+import About from "./pages/about";
 import RequestSupport from "./pages/request";
 import Opportunities from "./pages/opportunities";
 import Donate from "./pages/donate";
@@ -34,6 +35,7 @@ function Router() {
     <AppLayout>
       <Switch>
         <Route path="/" component={Home} />
+        <Route path="/about/:section?" component={About} />
         <Route path="/request" component={RequestSupport} />
         <Route path="/opportunities" component={Opportunities} />
         <Route path="/donate/:id" component={Donate} />