fix: import migration via web api body

scripts/spacetime-migration-common.mjs

@@ -133,6 +133,42 @@ export async function callSpacetimeProcedure(options, procedureName, input) {
   return parseProcedureResult(text);
 }
 
+export async function createSpacetimeWebIdentity(options) {
+  const serverUrl = resolveServerUrl(options).replace(/\/+$/u, '');
+  const url = `${serverUrl}/v1/identity`;
+  let response;
+  try {
+    response = await fetch(url, { method: 'POST' });
+  } catch (error) {
+    throw new Error(
+      `SpacetimeDB identity 请求失败: ${url}; ${error instanceof Error ? error.message : String(error)}`,
+    );
+  }
+
+  const text = await response.text();
+  if (!response.ok) {
+    throw new Error(`SpacetimeDB identity HTTP ${response.status}: ${trimPreview(text)}`);
+  }
+
+  let payload;
+  try {
+    payload = JSON.parse(text);
+  } catch (error) {
+    throw new Error(
+      `SpacetimeDB identity 响应不是合法 JSON: ${error instanceof Error ? error.message : String(error)}`,
+    );
+  }
+
+  const identity =
+    payload.identity ?? payload.Identity ?? payload.identity_hex ?? payload.identityHex;
+  const token = payload.token ?? payload.Token;
+  if (typeof identity !== 'string' || typeof token !== 'string') {
+    throw new Error(`SpacetimeDB identity 响应缺少 identity/token: ${trimPreview(text)}`);
+  }
+
+  return { identity, token };
+}
+
 export async function callSpacetimeProcedureAuto(options, procedureName, input) {
   if (options.useHttp) {
     return callSpacetimeProcedure(options, procedureName, input);
@@ -266,7 +302,7 @@ function normalizeTableStats(value) {
   });
 }
 
-function resolveServerUrl(options) {
+export function resolveServerUrl(options) {
   if (options.serverUrl) {
     return options.serverUrl;
   }