Fix documentation: corrected paths, improved clarity and updated backup instructions

[OlliesGudh]

The present PR is a follow-up of the #445 and actually brings the missing updates to some documentation pages that were not included in the previous PR.

Key corrections:

- Backing up your episodes page:

• Minor grammar fixes and clearer explanation of which data will be lost;
• Fixed the instruction path;
• Improved disclaimer to account for different Android versions and file pickers implementations.

- All my podcasts & episodes are gone page:

• Fixed paths in instructions;
• Removed the hyphen in backup;
• Updated Add local folder path to match Android's Scoped Storage while keeping backward compatibility with older versions.

PS: I am not sure about the formatting, but I tried to stay coherent with the writting style. Feedback appreciated.

[OlliesGudh]

@ByteHamster I’m still learning Git and accidentally pulled in extra commits unaware that they would be automatically included in the PR. They’re still relevant, but they will require further review, so I apologize for this mistake.

[ByteHamster]

Thanks!