Add comprehensive tests for client validation, revenue and expense categories, invoice generation, and schemas

- Implement tests for client validation functions including tax ID, VAT ID, IBAN, BIC, website, and company form validation.
- Create tests for revenue and expense categories ensuring all expected categories and labels are present.
- Add tests for invoice number generation with various scenarios including prefix handling and sequence padding.
- Introduce tests for default categories and their integration, ensuring no overlaps and consistent naming conventions.
- Implement Zod schema validation tests for currency, tax rates, IBAN, tax ID, VAT ID, invoices, companies, and customers.
- Add utility tests for tax calculations, including item amounts and invoice totals, ensuring correct handling of tax rates and formatting.
- Set up Vitest configuration and global test setup for consistent testing environment.

vitest.config.ts

@@ -0,0 +1,19 @@
+import { defineConfig } from "vitest/config";
+import react from "@vitejs/plugin-react";
+import tsconfigPaths from "vite-tsconfig-paths";
+
+export default defineConfig({
+  plugins: [react(), tsconfigPaths()],
+  test: {
+    environment: "jsdom",
+    globals: true,
+    setupFiles: ["./vitest.setup.ts"],
+    include: ["tests/**/*.test.ts", "tests/**/*.test.tsx"],
+    coverage: {
+      provider: "v8",
+      reporter: ["text", "json", "html"],
+      include: ["app/lib/**/*.ts", "app/lib/**/*.tsx"],
+      exclude: ["app/lib/**/*.server.ts"],
+    },
+  },
+});