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/components/ui/__tests__/badge.test.tsx

@@ -0,0 +1,15 @@
+import { describe, it, expect } from "vitest";
+import { render, screen } from "@testing-library/react";
+import { Badge } from "../badge";
+
+// Slice 1 harness smoke test: proves the Vitest + jsdom + Testing Library
+// harness runs and the new `success` Badge variant renders with the chart-2 cue.
+describe("Badge", () => {
+	it("renders a success variant tagged with the chart-2 cue", () => {
+		render(<Badge variant="success">Healthy</Badge>);
+		const badge = screen.getByText("Healthy");
+		expect(badge).toBeInTheDocument();
+		expect(badge.getAttribute("data-variant")).toBe("success");
+		expect(badge.className).toContain("bg-chart-2/10");
+	});
+});