feat: implement complete invoicing application with CSV import and PDF export

- Add comprehensive CSV import system with drag-and-drop upload and validation
- Create UniversalTable component with advanced filtering, searching, and batch actions
- Implement invoice management (view, edit, delete) with professional PDF export
- Add client management with full CRUD operations
- Set up authentication with NextAuth.js and email/password login
- Configure database schema with users, clients, invoices, and invoice_items tables
- Build responsive UI with shadcn/ui components and emerald branding
- Add type-safe API layer with tRPC and Zod validation
- Include proper error handling and user feedback with toast notifications
- Set up development environment with Bun, TypeScript, and Tailwind CSS

src/env.js

@@ -0,0 +1,48 @@
+import { createEnv } from "@t3-oss/env-nextjs";
+import { z } from "zod";
+
+export const env = createEnv({
+  /**
+   * Specify your server-side environment variables schema here. This way you can ensure the app
+   * isn't built with invalid env vars.
+   */
+  server: {
+    AUTH_SECRET:
+      process.env.NODE_ENV === "production"
+        ? z.string()
+        : z.string().optional(),
+    DATABASE_URL: z.string().url(),
+    NODE_ENV: z
+      .enum(["development", "test", "production"])
+      .default("development"),
+  },
+
+  /**
+   * Specify your client-side environment variables schema here. This way you can ensure the app
+   * isn't built with invalid env vars. To expose them to the client, prefix them with
+   * `NEXT_PUBLIC_`.
+   */
+  client: {
+    // NEXT_PUBLIC_CLIENTVAR: z.string(),
+  },
+
+  /**
+   * You can't destruct `process.env` as a regular object in the Next.js edge runtimes (e.g.
+   * middlewares) or client-side so we need to destruct manually.
+   */
+  runtimeEnv: {
+    AUTH_SECRET: process.env.AUTH_SECRET,
+    DATABASE_URL: process.env.DATABASE_URL,
+    NODE_ENV: process.env.NODE_ENV,
+  },
+  /**
+   * Run `build` or `dev` with `SKIP_ENV_VALIDATION` to skip env validation. This is especially
+   * useful for Docker builds.
+   */
+  skipValidation: !!process.env.SKIP_ENV_VALIDATION,
+  /**
+   * Makes it so that empty strings are treated as undefined. `SOME_VAR: z.string()` and
+   * `SOME_VAR=''` will throw an error.
+   */
+  emptyStringAsUndefined: true,
+});