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.

docs/ui-copy.md

@@ -73,7 +73,8 @@ Status: audit in progress for the 0.9.2 UI polish patch.
 
 ## Remaining audit work
 
-- Inventory hardcoded player-facing strings screen by screen and move them to `content/strings.en.json`.
+- Player-facing labels are now routed through `content/strings.en.json`; numeric
+  values, empty-state clears and debug-only text remain in code by design.
 - Verify focus/hover/pressed/disabled states with keyboard, gamepad and mouse.
 - Test long strings and 1.75x HUD font scale.
 - Capture every dialog/button state and run `screen_designs.py compare` plus the pinned judge.