test: Vitest setup + unit tests for API client, hooks, services + staff E2E

- Vitest + React Testing Library + MSW setup
- API client: 11 unit tests (fetch, errors, auth header, download, network failure)
- Service hooks: 26 tests across members, distributions, stock, dashboard, staff
- Custom hooks: 5 debounce tests (timer behavior, reset, custom delay)
- Components: 5 tests (offline banner, error boundary with retry)
- E2E: staff management page interactions
- npm scripts: test, test:run, test:coverage

cannamanage-frontend/vitest.config.ts

@@ -0,0 +1,19 @@
+import path from "path"
+
+import react from "@vitejs/plugin-react"
+import { defineConfig } from "vitest/config"
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: "jsdom",
+    globals: true,
+    setupFiles: ["./src/__tests__/setup.ts"],
+    include: ["src/**/*.{test,spec}.{ts,tsx}"],
+  },
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "./src"),
+    },
+  },
+})