test: enforce per-directory coverage thresholds

entities + use-cases + controllers must hit 100% (95% branches).
Project-wide baseline remains 80/75/80/80. Tightening these directories
reflects the architectural intent: these are the pure-logic layers and
should be exhaustively tested.

Added @vitest/coverage-v8@^3 to core-typescript, auth, blog,
marketing-pages, and navigation devDependencies.

Excluded from coverage (legitimately untestable):
- src/di/bind-production.ts — InversifyJS startup bootstrap
- src/application/repositories/** — pure TypeScript interfaces
- src/application/services/** — pure TypeScript interfaces (auth)
- src/integrations/cms/** — declarative Payload CMS config
- src/entities/cookie.ts — pure type aliases (auth)
- src/ui/** — React Query helpers, integration-tested in apps

Tests added (6 new files / 1 extended):
- auth/src/entities/errors.test.ts — UnauthenticatedError, UnauthorizedError,
  AuthenticationError, InputParseError constructors
- blog/src/entities/errors.test.ts — ArticleNotFoundError (default + custom
  message), InputParseError
- marketing-pages/src/entities/errors.test.ts — PageNotFoundError, InputParseError
- marketing-pages/src/entities/site-settings.test.ts — siteSettingsSchema
  (valid, no description, empty name rejection)
- navigation/src/entities/header.test.ts — headerItemSchema and headerSchema
  validation paths
- navigation/src/.../payload-header.repository.test.ts — logo relation-object,
  scalar-id, null, and null-item-field branches for full branch coverage

Spec: §6.9

packages/marketing-pages/src/entities/errors.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from "vitest";
+import { PageNotFoundError, InputParseError } from "./errors";
+
+describe("PageNotFoundError", () => {
+  it("uses the default message when none is given", () => {
+    const err = new PageNotFoundError();
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("Page not found");
+  });
+
+  it("uses a custom message when provided", () => {
+    const err = new PageNotFoundError("could not find page /about");
+    expect(err.message).toBe("could not find page /about");
+  });
+});
+
+describe("InputParseError", () => {
+  it("is an instance of Error with the given message", () => {
+    const err = new InputParseError("invalid input");
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("invalid input");
+  });
+});

packages/marketing-pages/src/entities/site-settings.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from "vitest";
+import { siteSettingsSchema } from "./site-settings";
+
+describe("siteSettingsSchema", () => {
+  it("accepts a valid site settings object", () => {
+    const result = siteSettingsSchema.parse({
+      siteName: "My Site",
+      siteDescription: "A great site",
+    });
+    expect(result.siteName).toBe("My Site");
+    expect(result.siteDescription).toBe("A great site");
+  });
+
+  it("accepts site settings without a description", () => {
+    const result = siteSettingsSchema.parse({ siteName: "My Site" });
+    expect(result.siteName).toBe("My Site");
+    expect(result.siteDescription).toBeUndefined();
+  });
+
+  it("rejects an empty siteName", () => {
+    expect(() => siteSettingsSchema.parse({ siteName: "" })).toThrow();
+  });
+});