chore: drop vestigial $lib alias

$lib pointed at src/lib/, which does not exist, and nothing imported it.
Removed the dead alias from all five declaration sites (tsconfig plus the
vite and three vitest configs). A stray $lib import now fails fast as an
unknown alias instead of resolving to a missing path.

vite.config.ts

@@ -6,7 +6,6 @@ export default defineConfig({
     plugins: [svelte(), tailwindcss()],
     resolve: {
         alias: {
-            $lib: '/src/lib',
             $app: '/src/app',
             $shared: '/src/shared',
             $entities: '/src/entities',