ci(i18n): detect unused & missing translation keys + clean en.json key debt

Rebased onto develop (post #1663 sentence-case pass). Adds a dependency-free
Bun checker (bun run i18n:check) wired into the lint matrix: flags keys used in
code but missing from en.json, and keys present in en.json but referenced
nowhere. Source-only - only en.json is checked/edited; Crowdin syncs the other
locales.

en.json: +8 missing source keys, -86 dead keys. Planned-feature keys kept and
allow-listed with tracking issues:
- home.settings.other.show_large_home_carousel (#1702 native media-bar)
- home.settings.logs.delete_all_logs (#1703 iOS logs fix)
- home.suggested_episodes (#1704)

login: point the TV password modal at the existing login.login_button instead
of a redundant login.login alias.

components/login/TVPasswordEntryModal.tsx

@@ -280,7 +280,7 @@ export const TVPasswordEntryModal: React.FC<TVPasswordEntryModalProps> = ({
               <View style={styles.buttonContainer}>
                 <TVSubmitButton
                   onPress={handleSubmit}
-                  label={t("login.login")}
+                  label={t("login.login_button")}
                   loading={isLoading}
                   disabled={!password}
                 />