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/vitest.config.ts

@@ -0,0 +1,22 @@
+import path from "path";
+import { defineConfig } from "vitest/config";
+import react from "@vitejs/plugin-react";
+
+// Vitest harness config (kept separate from vite.config.ts).
+// The `@` alias mirrors tsconfig.app.json (`"@/*": ["./src/*"]`).
+// test.include scopes Vitest to src/** component tests only; it must NOT claim
+// the frontend/tests/*.mjs node:test suites (run those via `npm run test:node`).
+export default defineConfig({
+	plugins: [react()],
+	resolve: {
+		alias: {
+			"@": path.resolve(__dirname, "./src"),
+		},
+	},
+	test: {
+		environment: "jsdom",
+		globals: true,
+		setupFiles: ["./src/test/setup.ts"],
+		include: ["src/**/*.{test,spec}.{ts,tsx}"],
+	},
+});