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/unit/utils.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+
+import { cn } from "@/lib/utils";
+
+describe("cn", () => {
+  it("joins truthy class values", () => {
+    expect(cn("a", "b")).toBe("a b");
+  });
+
+  it("ignores falsey values", () => {
+    expect(cn("a", false, null, undefined, "", "b")).toBe("a b");
+  });
+
+  it("supports conditional object syntax", () => {
+    expect(cn("base", { active: true, hidden: false })).toBe("base active");
+  });
+
+  it("merges conflicting tailwind classes, last wins", () => {
+    expect(cn("px-2", "px-4")).toBe("px-4");
+    expect(cn("text-sm text-red-500", "text-lg")).toBe("text-red-500 text-lg");
+  });
+
+  it("flattens arrays", () => {
+    expect(cn(["a", "b"], "c")).toBe("a b c");
+  });
+});