feat: support Cloud Mail email provider

- Merge the latest dev branch into PR #212 for a clean dev-targeted review base.

- Add Cloud Mail/SkyMail provider support for email generation and verification-code polling.

- Move Cloud Mail runtime logic into a dedicated background module and add docs plus regression tests.

tests/cloudmail-utils.test.js

@@ -0,0 +1,73 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const {
+  buildCloudMailHeaders,
+  getCloudMailTokenFromResponse,
+  normalizeCloudMailBaseUrl,
+  normalizeCloudMailDomain,
+  normalizeCloudMailDomains,
+  normalizeCloudMailMailApiMessages,
+} = require('../cloudmail-utils.js');
+
+test('normalizeCloudMailBaseUrl normalizes host and preserves path', () => {
+  assert.equal(
+    normalizeCloudMailBaseUrl('mail.example.com/api/'),
+    'https://mail.example.com/api'
+  );
+  assert.equal(
+    normalizeCloudMailBaseUrl('http://127.0.0.1:8080'),
+    'http://127.0.0.1:8080'
+  );
+  assert.equal(normalizeCloudMailBaseUrl('::::'), '');
+});
+
+test('normalizeCloudMailDomain and domains de-duplicate valid entries', () => {
+  assert.equal(normalizeCloudMailDomain('@Mail.Example.com'), 'mail.example.com');
+  assert.equal(normalizeCloudMailDomain('not-a-domain'), '');
+  assert.deepEqual(
+    normalizeCloudMailDomains(['mail.example.com', 'MAIL.EXAMPLE.COM', 'bad-value']),
+    ['mail.example.com']
+  );
+});
+
+test('buildCloudMailHeaders includes token and content type when needed', () => {
+  assert.deepEqual(
+    buildCloudMailHeaders({ token: 'token-value' }, { json: true }),
+    {
+      Authorization: 'token-value',
+      'Content-Type': 'application/json',
+      Accept: 'application/json',
+    }
+  );
+});
+
+test('normalizeCloudMailMailApiMessages extracts rows from nested Cloud Mail payloads', () => {
+  const messages = normalizeCloudMailMailApiMessages({
+    data: {
+      records: [
+        {
+          emailId: 'mail-1',
+          toEmail: 'User@Example.com',
+          sendEmail: 'noreply@tm.openai.com',
+          subject: 'OpenAI verification code',
+          content: '<p>Your code is <strong>654321</strong> &amp; ready.</p>',
+          createTime: '2026-05-07 10:20:00',
+        },
+      ],
+    },
+  });
+
+  assert.equal(messages.length, 1);
+  assert.equal(messages[0].id, 'mail-1');
+  assert.equal(messages[0].address, 'user@example.com');
+  assert.equal(messages[0].from.emailAddress.address, 'noreply@tm.openai.com');
+  assert.match(messages[0].bodyPreview, /654321/);
+  assert.match(messages[0].bodyPreview, /& ready/);
+  assert.equal(messages[0].receivedDateTime, '2026-05-07T10:20:00.000Z');
+});
+
+test('getCloudMailTokenFromResponse supports direct and nested response shapes', () => {
+  assert.equal(getCloudMailTokenFromResponse({ token: 'one' }), 'one');
+  assert.equal(getCloudMailTokenFromResponse({ data: { accessToken: 'two' } }), 'two');
+});