refactor(marketing-pages): factory-style use cases + per-use-case controllers

- Use cases (get-page-by-slug, get-site-settings) → factory functions with I*UseCase aliases
- Controllers split: pages.controller.ts → 2 single-responsibility files
- DI module wires factories with .toDynamicValue()
- tRPC router resolves controllers via container

Refactor log: §2, §3, §4.1, §4.2, §5.1
Spec: §6.3

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/marketing-pages/src/interface-adapters/controllers/get-page-by-slug.controller.test.ts

@@ -0,0 +1,35 @@
+import { describe, it, expect } from "vitest";
+import { getPageBySlugController } from "@/interface-adapters/controllers/get-page-by-slug.controller";
+import { getPageBySlugUseCase } from "@/application/use-cases/get-page-by-slug.use-case";
+import { MockPagesRepository } from "@/infrastructure/repositories/pages.repository.mock";
+import { InputParseError } from "@/entities/errors/common";
+
+describe("getPageBySlugController", () => {
+  it("returns the page when found", async () => {
+    const repo = new MockPagesRepository();
+    const useCase = getPageBySlugUseCase(repo);
+    const controller = getPageBySlugController(useCase);
+
+    const result = await controller({ slug: "about" });
+    expect(result?.slug).toBe("about");
+  });
+
+  it("throws InputParseError on missing slug", async () => {
+    const repo = new MockPagesRepository();
+    const useCase = getPageBySlugUseCase(repo);
+    const controller = getPageBySlugController(useCase);
+
+    await expect(
+      controller({} as { slug: string }),
+    ).rejects.toBeInstanceOf(InputParseError);
+  });
+
+  it("returns undefined when slug not found", async () => {
+    const repo = new MockPagesRepository();
+    const useCase = getPageBySlugUseCase(repo);
+    const controller = getPageBySlugController(useCase);
+
+    const result = await controller({ slug: "nonexistent" });
+    expect(result).toBeUndefined();
+  });
+});