feat(auth): bring opaque (RFC 9807) auth

OPAQUE (RFC 9807) implementation (using `opaque-ke` crate)

    with opaque authentfication, server will never receive the password (in the auth=password mode)
    this is a must have to create trust with users to permit end to end encryption in the future
    (we cannot know if user use the same password/passphrase for his asymetric key or his oxicloud auth,
    this is why server must never have the password)

    pass1: prepare server

frontend/package.json

@@ -45,5 +45,8 @@
     "vite": "^6.4.3",
     "vite-plugin-istanbul": "^8.0.0",
     "vitest": "^4.1.9"
+  },
+  "dependencies": {
+    "@serenity-kit/opaque": "^1.1.0"
   }
 }