Add version number display to UI header

Inject app version (v1.0.0) at build time via Vite define config
and display it below the title in muted text.

app/src/App.tsx

@@ -102,9 +102,10 @@ function App() {
           />
         </>
       )}
-      <h1 style={{ fontSize: '20px', marginBottom: '12px', color: '#111' }}>
+      <h1 style={{ fontSize: '20px', marginBottom: '2px', color: '#111' }}>
         EMBA Specialization Solver
       </h1>
+      <div style={{ fontSize: '11px', color: '#999', marginBottom: '12px' }}>v{__APP_VERSION__}</div>
 
       <ModeToggle mode={state.mode} onSetMode={setMode} />
 

app/src/vite-env.d.ts

@@ -0,0 +1,3 @@
+/// <reference types="vite/client" />
+
+declare const __APP_VERSION__: string;