feat: make product features a declared selection with a runtime kill switch

Which features a build contains was not a decision anybody could express. The
reference feature was spread directly into the route, API, schema, codec and
adapter registries, so shipping without it meant editing five files by hand and
hoping nothing still referred to it — and there was no way at all to take it out
of service on a running deployment. The removability gate proved the editing
worked; nothing made it a choice.

There is now one manifest. `VITE_PRODUCT_FEATURES` narrows it at build time and
`FEATURE_OVERRIDES` in the runtime document takes an installed feature out of
service without a rebuild. Every registry composes from the manifest, and a test
fails if a new one forgets to.

Both inputs are subtractive, and the vocabulary is what enforces it rather than
a check somewhere downstream: the override enum has no `ENABLED`, and a
build-time selection naming something the source tree does not declare is
refused instead of ignored. A configuration document that could name a feature
into existence would be a configuration document choosing which code runs.

Disabling is not just hiding. Withdrawing a route from navigation would leave a
typed deep link that still mounts the feature, so the router refuses it too and
answers with a surface that says the deployment switched it off. The platform
overview now distinguishes the three states an operator actually needs: serving,
switched off, and not in this build.

What this is not: an env var does not shrink the bundle. A static import cannot
be undone by a value, and making the import graph itself depend on a
configuration string is the thing §3.5 exists to prevent — measured, `none`
changes the output by 58 bytes. Physical removal remains FE-GATE-020's job, and
the code comments say so rather than implying otherwise.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/presentation/i18n/catalog.ts

@@ -79,6 +79,10 @@ const PLATFORM_KO_MESSAGES = {
   "route.invalid.title": "올바르지 않은 주소입니다.",
   "route.invalid.description": "주소의 경로 또는 검색 조건을 확인해 주세요.",
   "route.invalid.action": "안전한 탐색 링크를 사용해 주세요.",
+  "route.disabledFeature.title": "현재 사용할 수 없는 기능입니다.",
+  "route.disabledFeature.description":
+    "이 기능은 배포 설정에서 중지되어 있습니다. 코드에는 포함되어 있으며 운영자가 다시 켤 수 있습니다.",
+  "route.disabledFeature.action": "다른 탐색 링크를 사용해 주세요.",
   "route.auth.integration.title": "로그인 연동이 필요합니다.",
   "route.auth.integration.description":
     "외부 인증 소유자가 연결되면 이 보호 라우트를 사용할 수 있습니다.",
@@ -233,6 +237,10 @@ const PLATFORM_EN_MESSAGES = {
   "route.invalid.title": "This address is invalid.",
   "route.invalid.description": "Check the path and search parameters.",
   "route.invalid.action": "Use a safe navigation link.",
+  "route.disabledFeature.title": "This feature is not available right now.",
+  "route.disabledFeature.description":
+    "The deployment configuration has switched it off. It is still part of this build and an operator can switch it back on.",
+  "route.disabledFeature.action": "Use another navigation link.",
   "route.auth.integration.title": "Sign-in integration is required.",
   "route.auth.integration.description":
     "This protected route is available after an external authentication owner is connected.",