Users can now sign in with name + password on a device that has never seen the
account by opting into a cloud backup at account creation. The seed phrase is
locally re-wrapped with scrypt + AES-GCM keyed by the password and published
as a NIP-78 kind:30078 event under d-tag `hermes.backup.v1/<sha256(name)>`.
Relays only ever see opaque ciphertext; the password is the only decryption
key, so backup strength is password strength.
Signin tries the local wrap first (fast, no network) and falls back to the
cloud copy if the device hasn't been used before. Settings → Backup now has
"Back up to cloud" / "Re-upload" / "Remove cloud backup" controls that reuse
the Reveal-seed password field as the key.
Site: added @media breakpoints to shared.css so the header collapses cleanly
on narrow screens (icon-only brand under 380px, hidden "Sign in" label under
640px), the hero mark drops to 84px, h1 scales down, and buttons shrink to
touch sizes. Also fixed a stale reference to the removed `mnemonicBox` id in
the Create-account toggle that was throwing a TypeError on mobile.
bbe5d3d298