v1.5.1: docs and e2e fixes for OSS send + sync

Real e2e tests verified against deployed test worker: /api/send
outbound recording, /api/sync to local sqlite with search/code/attachments.
Updated skill.md and all 3 READMEs with sync command and /api/send docs.

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

Author: guo-yu

package.json

@@ -1,6 +1,6 @@
 {
   "name": "mails",
-  "version": "1.5.0",
+  "version": "1.5.1",
   "description": "Email infrastructure for AI agents",
   "type": "module",
   "main": "dist/index.js",

src/cli/index.ts

@@ -39,7 +39,7 @@ async function main() {
     case 'version':
     case '--version':
     case '-v':
-      console.log('mails v1.5.0')
+      console.log('mails v1.5.1')
       break
     default:
       console.error(`Unknown command: ${command}`)