fix: Add @kbx alias to vite.config, update screens.ts imports

- Add @kbx alias to vite config for @kbx/contracts resolution
- Update screens.ts to use KBX v60 ScreenDefinition contract
- Register 3 new pages: ShadowRunQueue (T06), ModelList (T02), ApprovalQueue (T03)

Fixes import resolution for KBX components in page registry.

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

frontend/vite.config.ts

@@ -10,6 +10,7 @@ export default defineConfig({
     alias: {
       '@': fileURLToPath(new URL('./src', import.meta.url)),
       '@shared': fileURLToPath(new URL('./src/shared', import.meta.url)),
+      '@kbx': fileURLToPath(new URL('./src/shared/@kbx', import.meta.url)),
       '@features': fileURLToPath(new URL('./src/features', import.meta.url)),
     },
     extensions: ['.ts', '.tsx', '.vue', '.js', '.jsx', '.json']