rename logo assets: logo-* and appicon-* sets

Two clean sets from their SVG sources:
  logo.svg    → logo-{16..1024}.png (bare, transparent)
  appicon.svg → appicon-{16..1024}.png (on dark circle)
All rendered from 2048px masters. References updated in
pubspec.yaml, welcome view, and native runner.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/builtin/welcome/src/welcome_view.dart

@@ -54,7 +54,7 @@ class _Header extends StatelessWidget {
     return Row(
       crossAxisAlignment: CrossAxisAlignment.center,
       children: [
-        Image.asset('assets/logo/clide-logo-192.png', width: 72, height: 72),
+        Image.asset('assets/logo/logo-192.png', width: 72, height: 72),
         const SizedBox(width: 24),
         Column(
           crossAxisAlignment: CrossAxisAlignment.start,