test: add comprehensive automated test coverage

- Vitest multi-project setup (unit / integration / component)
- Real-Postgres integration harness via in-process PGlite (TEST_DATABASE_URL
  override), migrations applied per worker; production code untouched
- Unit: routing, locale, validation/Zod schemas, metadata, mail, site-theme,
  marquee, media, portfolio helpers, plus architecture-rule tests
- Integration: Prisma data layer, API routes, and all server actions
- Component: UI primitives and form components (jsdom + Testing Library)
- 371 tests passing

tests/helpers/next-mocks.ts

@@ -0,0 +1,67 @@
+import { vi } from "vitest";
+
+/**
+ * Shared mocks for the Next.js runtime pieces that server actions depend on.
+ * Action tests wire these in with `vi.mock(...)` at the top of each file, e.g.:
+ *
+ *   vi.mock("next/navigation", async () => ({
+ *     redirect: (await import("@/tests/helpers/next-mocks")).redirect,
+ *   }));
+ */
+
+export class RedirectError extends Error {
+  readonly digest = "NEXT_REDIRECT";
+  readonly __isRedirect = true;
+  constructor(public url: string) {
+    super(`NEXT_REDIRECT:${url}`);
+  }
+}
+
+export function redirect(url: string): never {
+  throw new RedirectError(url);
+}
+
+export function isRedirectError(error: unknown): error is RedirectError {
+  return (
+    error instanceof RedirectError ||
+    (typeof error === "object" && error !== null && (error as { __isRedirect?: boolean }).__isRedirect === true)
+  );
+}
+
+export const revalidatePath = vi.fn();
+
+export const adminAuth = { authenticated: true };
+export const clearAdminSessionCookie = vi.fn(async () => {});
+export async function isAdminAuthenticated(): Promise<boolean> {
+  return adminAuth.authenticated;
+}
+
+/** Run an action and return the URL it redirected to (or throw if it didn't). */
+export async function captureRedirect(run: () => Promise<unknown>): Promise<string> {
+  try {
+    await run();
+  } catch (error) {
+    if (isRedirectError(error)) {
+      return error.url;
+    }
+    throw error;
+  }
+  throw new Error("Expected the action to redirect, but it returned normally.");
+}
+
+export function resetNextMocks() {
+  revalidatePath.mockClear();
+  clearAdminSessionCookie.mockClear();
+  adminAuth.authenticated = true;
+}
+
+/** Build a FormData from a flat record (strings and Files). */
+export function formDataFrom(fields: Record<string, string | File | undefined>): FormData {
+  const formData = new FormData();
+  for (const [key, value] of Object.entries(fields)) {
+    if (value !== undefined) {
+      formData.set(key, value);
+    }
+  }
+  return formData;
+}