How this works: The URL contains a Blossom blob address and an
encryption key after the # symbol. The key never leaves your browser — the server
only sees an opaque encrypted blob. This page downloads the blob, decrypts it
locally using ChaCha20-Poly1305, and offers the decrypted file for download.
Privacy: The encryption key (after #) is never sent to any server.
Per RFC 3986, URL fragments are client-side only.