Update prevent-auto-update guide for MTP and current scripts

[iiroak]

Summary

Rewrites the Prevent automatic updates guide to match the current Kindle-Filler-Disk tool and today's Kindle lineup. Rebased on current main; single-file change to content/jailbreaking/prevent-auto-update/__index.md.

• MTP support: the previous guide said the script does not work on 11th gen+; it now covers Mass Storage AND MTP (11th gen+, PW5/6, Scribe, Basic 2024) with auto-detection.
• Run on the computer: one-liner (irm/curl) using the current Scripts/Filler.ps1 / Filler.sh, instead of copying the script onto the Kindle.
• Update-size reference: table of the exact current firmware sizes (fetched from Amazon's download servers, ~212 MB up to ~489 MB) and a recommended max free space to reliably block OTA.
• 100 MB file layout: explains deleting a single 100 MB file to add a book without unblocking OTA.
• Fallbacks: pre-built ZIP fallback + manual-copy links, and a GUI alternative (jannikac/mtp-filler).
• Updates repo links from bastianmarin to iiroak.

Note

The ZIP fallback / manual-copy links point to iiroak/Kindle-Filler-Disk/raw/main/Zips/, which still needs the Zips/ archives pushed to resolve; the rest of the guide is fully functional.