refactor(marketing-pages): unify use-case I/O schemas + presenter + feature error map

Per Plan 9 (spec R1-R28):
- Use cases: input + output schemas (getPageBySlug, getSiteSettings).
  Site-settings input is z.object({}).strict() per R5 (uniform input).
- Controllers: unknown input + identity presenter; void output not
  applicable (both use cases return data).
- New integrations/api/procedures.ts with marketingPagesProcedure
  ([InputParseError → BAD_REQUEST], [PageNotFoundError → NOT_FOUND]).
- Router uses marketingPagesProcedure + .input(xInputSchema).
- src/index.ts: remove pageBySlugQuery/siteSettingsQuery; export
  schemas + types + IUseCase/IController aliases.
- src/ui/index.ts (NEW); package.json adds ./ui subpath.
- R25 output-validation tests + R26 router error-mapping test.

Refactor log: §1, §2, §3.1, §3.2, §3.3, §5.1, §5.2, §6.1, §6.2
Spec: R1–R6, R8–R15, R18–R20, R22–R26

packages/marketing-pages/src/index.ts

@@ -3,4 +3,23 @@ export type { SiteSettings } from "./entities/models/site-settings";
 export type { MarketingPagesRouter } from "./integrations/api/router";
 export { PageNotFoundError } from "./entities/errors/page";
 export { InputParseError } from "./entities/errors/common";
-export { pageBySlugQuery, siteSettingsQuery } from "./ui/query";
+
+// Use case schemas + types (Plan 9 R18)
+export {
+  getPageBySlugInputSchema,
+  getPageBySlugOutputSchema,
+  type GetPageBySlugInput,
+  type GetPageBySlugOutput,
+  type IGetPageBySlugUseCase,
+} from "./application/use-cases/get-page-by-slug.use-case";
+export {
+  getSiteSettingsInputSchema,
+  getSiteSettingsOutputSchema,
+  type GetSiteSettingsInput,
+  type GetSiteSettingsOutput,
+  type IGetSiteSettingsUseCase,
+} from "./application/use-cases/get-site-settings.use-case";
+
+// Controller type aliases
+export type { IGetPageBySlugController } from "./interface-adapters/controllers/get-page-by-slug.controller";
+export type { IGetSiteSettingsController } from "./interface-adapters/controllers/get-site-settings.controller";