- Migrate theme persistence from `sessionStorage` to `localStorage`
- Rename theme HTML attribute to `data-bs-theme` for Bootstrap compatibility
- Trim and compile CSS according to the chosen theme mode
* Add common German date format.
* Fix translation of read time prompt to a more correct word.
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Co-authored-by: Cotes Chung <11371340+cotes2020@users.noreply.github.com>