fix: reference vite/client types for TypeScript 6 compatibility

TypeScript 6 enables noUncheckedSideEffectImports by default, so
side-effect CSS imports need declarations, which vite/client provides.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Florent Benoit <fbenoit@redhat.com>
Change-Id: Ib12805cb8758b2695f34e13a2ba2d15cb40d6cde

Author: benoitf

src/app.d.ts

@@ -17,6 +17,7 @@
  ***********************************************************************/
 
 /// <reference types="svelte" />
+/// <reference types="vite/client" />
 
 // See https://kit.svelte.dev/docs/types#app
 // for information about these interfaces