fix: use Express 5 compatible catch-all route syntax

Change SPA fallback from app.get('*') to app.get('/{*splat}')
as Express 5 uses path-to-regexp v8+ which requires named splat.

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

server/src/index.ts

@@ -100,7 +100,8 @@ async function boot(): Promise<void> {
   }
 
   // SPA Fallback (MUST be after plugin routes)
-  app.get('*', (_req, res) => {
+  // Express 5 uses path-to-regexp v8+ which requires named splat syntax
+  app.get('/{*splat}', (_req, res) => {
     res.sendFile(path.join(import.meta.dirname ?? __dirname, '..', '..', 'web', 'dist', 'index.html'));
   });