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

Per Plan 9 (spec R1-R28):
- getHeader use case: input z.object({}).strict() (R5); output =
  headerSchema parsed at runtime.
- getHeader controller: unknown input + identity presenter.
- New integrations/api/procedures.ts with navigationProcedure
  ([InputParseError → BAD_REQUEST], [HeaderNotFoundError → NOT_FOUND]).
- Router uses navigationProcedure + .input(getHeaderInputSchema).
- src/index.ts: remove headerQuery; export schemas + IUseCase/Controller
  aliases.
- src/ui/index.ts (NEW); package.json adds ./ui subpath.
- R25 + R26 tests added.

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/navigation/package.json

@@ -5,6 +5,7 @@
   "type": "module",
   "exports": {
     ".": "./src/index.ts",
+    "./ui": "./src/ui/index.ts",
     "./cms": "./src/integrations/cms/index.ts",
     "./api": "./src/integrations/api/router.ts",
     "./di/bind-production": "./src/di/bind-production.ts"