fix: use logo-signin, consolidate plane asset, fix home marker on resize

- Sign-in page now uses logo-signin.png
- World map animation uses airplane.png; remove unused animationPlane.png
- Re-project home marker on map resize so it stays correct when stats panel collapses

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

src/lib/auth/LoginOverlay.svelte

@@ -1,6 +1,6 @@
 <script>
   import { signInWithGoogle } from './userStore.svelte.js';
-  import logoImg from '../../assets/logo.png';
+  import logoImg from '../../assets/logo-signin.png';
 </script>
 
 <div class="overlay">