Aaina Desktop v0.1.3

Safety fixes from an independent review.

• The app can only use its own folders, your photos folder (Pictures/Aaina), Downloads, and files or folders you choose or drag onto the window. It no longer has access to your whole home folder. A folder you choose stays allowed after a restart.
• Restoring a backup can't choose where files go: its photos are copied into your current photos folder, nothing already there is overwritten, and a folder that isn't a real Aaina backup is refused.
• The studio catalogue can only save files inside its own cache folder.
• Photos are always drawn again before they are sent to OpenAI, so location, camera and date details in the file are never sent.
• "New version available" only ever opens this project's release page.
• Each release now has a SHA256SUMS.txt checksum list and GitHub's signed proof of where every file was built (check one with gh attestation verify <file> -R aaina-world/aaina-desktop). A release is only built after every check passes on that exact version.
  Builds are unsigned for now; your system may warn the first time you open the app (see the README).