CI4 4.3.1 upgrade

- add missing files
- overwrite changed files
- merge code changes
- Matched .htaccess file in /public/ to CI4
- Corrected naming of Error language file to Errors
- Refactored references to Error language file
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f