Row 332 R2 (#1830): give the federation acceptance hosts a fake pi key

GPT review F1: prepare() built the host env from HOME, PATH, TMPDIR,
MOSAIC_CONFIG and NODE_EXTRA_CA_CERTS only, so the pi credential preflight
refused the assistant launch (no-session-credential) and the RESULT wait
failed. scripts/test-federation-acceptance.sh red on 6e9f3d723, green with
the fake ZAI_API_KEY the cli tests use.

packages/cli/tests/federation-acceptance.test.mjs

@@ -119,7 +119,7 @@ function prepare(name, iss, ca) {
   git('add', 'file.txt'); git('commit', '-q', '-m', 'scratch fixture');
   const adapter = join(fixtureRoot, 'adapter.sh');
   writeFileSync(adapter, `exec '${process.execPath}' '${adapterModule}'\n`);
-  return { name, origin, configDir, dataRoot, adapter, env: { ...env, MOSAIC_CONFIG: config, NODE_EXTRA_CA_CERTS: ca }, port: null };
+  return { name, origin, configDir, dataRoot, adapter, env: { ...env, MOSAIC_CONFIG: config, NODE_EXTRA_CA_CERTS: ca, ZAI_API_KEY: 'fx332-fake-pi' }, port: null };
 }
 
 async function signIn(instance, op, iss, sub) {