build(web): add TanStack Query + Testing Library deps

Wires @tanstack/svelte-query for the data layer and
@testing-library/{svelte,jest-dom} for component-level tests. Registers
the jest-dom matchers via a new vitest setup file.

web/vitest.setup.ts

@@ -0,0 +1 @@
+import '@testing-library/jest-dom/vitest';