Add Index.html and Preview.html in Default for Typo3 backend

[RZivaralam]

TYPO3 13 changed the way backend templates are resolved.
In TYPO3 12, the extension correctly found templates in their subfolders (e.g., TKControlPanelModule/SolarModule).
In TYPO3 13, the same setup causes a "Default/Index.html" lookup error.

To fix this for TYPO3 13 without breaking existing functionality:

• Added Index.html and Preview.html to the Default/ folder.

This ensures that the backend modules can render properly, while keeping the original structure intact.
Maintainers can review and decide if this approach should be applied in the main branch permanently or if a more structured solution is needed in the future.

[dkd-kaehm]

Why adding/copying and not moving the files?

[RZivaralam]

I decided to copy the files instead of moving them because I wasn’t completely sure if the existing template files are still being used by the extension or other parts of the module.

To avoid breaking any existing functionality or references, I added the new templates under Default/ as a safe workaround.

---

I also removed the old Backend folder, and the module still works correctly after this change.

However, I’m not completely sure if those files might still be used somewhere else in the extension.

You probably know the plugin’s structure better than I do, so please double-check if this removal is safe.

From my tests, the connection and the backend module are working fine with the new Default/ templates. without backend folder