feat: add credentials file output

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

.gitignore

···
 .wrangler/
 node_modules/
+credentials-*.json

scripts/setup.js

···
  */
 
 import { webcrypto } from 'crypto'
+import { writeFileSync } from 'fs'
 
 // === ARGUMENT PARSING ===
 
···
   return true
 }
 
+// === CREDENTIALS OUTPUT ===
+
+function saveCredentials(filename, credentials) {
+  writeFileSync(filename, JSON.stringify(credentials, null, 2))
+}
+
 // === MAIN ===
 
 async function main() {
···
     console.log('  Relay notified!')
   }
   console.log('')
+
+  // Step 6: Save credentials
+  const credentials = {
+    handle: fullHandle,
+    did,
+    privateKeyHex: bytesToHex(keyPair.privateKey),
+    didKey,
+    pdsUrl: opts.pds,
+    createdAt: new Date().toISOString()
+  }
+
+  const credentialsFile = `./credentials-${opts.handle}.json`
+  saveCredentials(credentialsFile, credentials)
+
+  // Final output
+  console.log('Setup Complete!')
+  console.log('===============')
+  console.log(`Handle: ${fullHandle}`)
+  console.log(`DID: ${did}`)
+  console.log(`PDS: ${opts.pds}`)
+  console.log('')
+  console.log(`Credentials saved to: ${credentialsFile}`)
+  console.log('Keep this file safe - it contains your private key!')
 }
 
 main().catch(err => {