v1.2.1: auto-resolve mailbox from api_key via /v1/me

- `mails config set api_key mk_xxx` now auto-fetches mailbox + default_from
- resolveApiKey() shared by config, storage, and send modules
- Full E2E tests for both hosted (mails.dev) and self-hosted (test.mails.dev)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: guo-yu

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mails",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "Email infrastructure for AI agents",
   "type": "module",
   "main": "dist/index.js",

src/cli/index.ts

@@ -35,7 +35,7 @@ async function main() {
     case 'version':
     case '--version':
     case '-v':
-      console.log('mails v1.2.0')
+      console.log('mails v1.2.1')
       break
     default:
       console.error(`Unknown command: ${command}`)