feat(ext/setup): add device name step to setup wizard

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>

extension/src/wasm.d.ts

@@ -60,6 +60,9 @@ declare module 'relicario-wasm' {
 
   export function totp_compute(config_json: string, now_unix_seconds: bigint): TotpCode;
 
+  export function generate_device_keypair(): string;
+  export function get_field_history(item_json: string): unknown;
+
   export default function init(module_or_path?: unknown): Promise<void>;
   export function initSync(args: { module: WebAssembly.Module }): void;
 }