fix(import): Add $state to fileInput for reactivity

Fix Svelte non_reactive_update warning by declaring fileInput
with $state() since it's updated during component lifecycle.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: justjuangui

src/lib/ui/ImportDialog.svelte

@@ -43,7 +43,7 @@
 
   // Dialog ref
   let dialog: HTMLDialogElement;
-  let fileInput: HTMLInputElement | null = null;
+  let fileInput = $state<HTMLInputElement | null>(null);
 
   // Import mode
   let importMode = $state<ImportMode>("file");