New step 4 after vault creation: enter device name (defaults to
"Chrome on Linux" based on detected browser/OS). Generates ed25519
keypair, stores private key in chrome.storage.local, registers
device with vault. Wizard is now 5 steps (was 4).
Also adds generate_device_keypair() to wasm.d.ts type declarations.
Co-Authored-By: Claude <noreply@anthropic.com>
eb14946f06