memoize t in the typed wrappers, and give app code typed access to ui.*

Each wrapper built a fresh closure every render, so `t` in a dependency array
recomputed forever. That is the documented useClient()/Jellyfin trap in
platform/CLAUDE.md, and phase 2 needs t in useMemo deps immediately.

useTranslation in officer-web now also returns tUi, typed against the shared
components' catalog. 'Cancel' and 'Close' recur across the shell and already exist
in ui.* — the alternative was importing two hooks in a hundred files.

src/apps/officer-web/lib/i18n.ts

@@ -1,14 +1,32 @@
 import type { TranslationKeys } from 'i18n';
 import type { InterpolationParams } from 'i18n';
+import { useCallback } from 'react';
 import { useTranslation as useTranslationBase } from 'i18n';
 import type en from '../locales/en-GB.json';
+import type uiEn from '@/components/locales/en-GB.json';
 
 type AppTranslationKey = TranslationKeys<typeof en>;
+type UiTranslationKey = TranslationKeys<typeof uiEn>;
 
-// The `app.` prefix is namespace wiring for the merged catalog (D6) — callers never spell it, they
-// pass the same bare key the JSON file uses.
+/**
+ * `t` for this workspace's own catalog, `tUi` for the shared-component one.
+ *
+ * Both are here rather than in two imports because "Cancel", "Close" and "Search" recur across the
+ * shell and genuinely belong to `ui.*` — phase 1 put them there so phases 2 and 3 could reach for them
+ * instead of inventing a second key for the same word. Anything feature-specific stays in `app.*`:
+ * per D6 a `ui.*` key may not name a feature.
+ *
+ * Both are memoized. An unstable `t` is unusable in a dependency array, and this repo has already lost
+ * days to exactly that shape — see platform/CLAUDE.md on `useClient()` and the Jellyfin player.
+ */
 export const useTranslation = () => {
   const { t: baseT, locale } = useTranslationBase();
-  const t = (key: AppTranslationKey, params?: InterpolationParams) => baseT(`app.${key}`, params);
-  return { t, locale };
+
+  const t = useCallback((key: AppTranslationKey, params?: InterpolationParams) => baseT(`app.${key}`, params), [baseT]);
+
+  const tUi = useCallback((key: UiTranslationKey, params?: InterpolationParams) => baseT(`ui.${key}`, params), [baseT]);
+
+  return { t, tUi, locale };
 };
+
+export type { AppTranslationKey };