feat(frontend): slice 1 — foundation for MUI->shadcn migration

Web UI rework (openspec/changes/web-ui-rework). Foundation slice:
- Add @tanstack/react-table; remove orphaned recharts, d3
- Vendor shadcn primitives: tabs table dialog input label checkbox
  switch progress separator avatar textarea dropdown-menu scroll-area
- Add Vitest + @testing-library/react + jsdom harness; npm test script
- Delete no-op theme.ts shim; remove getAppTheme references
- Smoke test proves the harness

Gate: build + lint + test green.

frontend/src/test/setup.ts

@@ -0,0 +1,5 @@
+// Vitest global setup: registers @testing-library/jest-dom matchers
+// (toBeInTheDocument, toHaveAttribute, …) for the jsdom environment.
+// The `/vitest` entry both registers the matchers at runtime and provides the
+// TypeScript module augmentation for vitest's `expect` so tsc typechecks them.
+import "@testing-library/jest-dom/vitest";