Route UI labels through the string table

Move start menu, settings, pause, Help, HUD, radio, shift review and campaign
labels/templates into content/strings.en.json, including placeholder-validated
dynamic status text. No player-facing hardcoded labels remain outside dynamic
data/debug output. Headless 250/250, docs check OK.

TODO.md

@@ -60,8 +60,9 @@ screen-design judge before any model/texture changes. No gameplay rules change.
 - [x] Audit all button labels for verb-first wording, capitalization, ordering,
       destructive-action confirmation and consistent confirm/cancel placement;
       recorded in `docs/ui-copy.md` and fixed Quit/Apply wording.
-- [ ] List every hardcoded player-facing string and route it through
-      `content/strings.en.json`; add placeholder validation for new keys.
+- [x] List every hardcoded player-facing string and route it through
+      `content/strings.en.json`; remaining UI literals are numeric/debug-only or
+      dynamic data. Placeholder validation covers the new keys.
 - [ ] Review NPC/door-staff/radio/tutorial/help/review/campaign dialogue for
       repetition, ambiguity, tone and localization length.