fix: add missing default string resources

[a1denvalu3]

Summary

• Added missing default string values to app/src/main/res/values/strings.xml to fix build warnings.
• Resolves issues where translated strings (e.g., pt, es) were defined without an English fallback, ensuring proper fallback on devices using unconfigured locales.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 20.62%. Comparing base (22b7b9f) to head (236d88b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #261      +/-   ##
============================================
- Coverage     20.64%   20.62%   -0.02%     
+ Complexity      773      771       -2     
============================================
  Files           145      145              
  Lines         18575    18575              
  Branches       2274     2274              
============================================
- Hits           3834     3832       -2     
+ Misses        14261    14260       -1     
- Partials        480      483       +3     

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