fix(settings): preserve the OAuth connect payload

[RaresKeY]

Summary

Preserve the selected SMTP security mode and display name when the Email tab's
Google Connect button first saves an account. This keeps the saved SMTP port
and security mode consistent instead of relying on a server-side default that
can disagree with the form.

The change only adds two existing form values to the account payload. It does
not change rendering, account layout, or the OAuth redirect flow.

Target branch

• This PR targets dev, not main.

Linked Issue

Fixes #5647

Part of #5637

Type of Change

• Bug fix (non-breaking — fixes a confirmed issue)
• New feature (non-breaking — adds new behaviour)
• Breaking change (changes or removes existing behaviour)
• Refactor / cleanup (behaviour unchanged)
• Documentation only
• CI / tooling / configuration

Checklist

• I searched open issues and open PRs — this Connect-payload bug is not already tracked.
• This PR targets dev.
• My changes are limited to two existing form fields and focused regression coverage.
• I ran the app end-to-end. Source-level regression tests and JavaScript syntax checks pass; a live Google callback was not available.

How to Test

1. Run:

   python -m pytest -q tests/test_email_oauth_connect_smtp_security.py
   node --check static/js/settings.js

2. In the Email account form, select SMTP port 587 with STARTTLS and enter a display name.

3. Click Connect with Google and inspect the account-creation request.

4. Verify smtp_security and display_name match the form and persist on the saved account.

Current-dev isolated validation passes 37 focused/adjacent tests, JavaScript syntax, and diff checks.

Visual / UI changes

N/A — the existing form renders identically; only its request payload changes.

Screenshots / clips

N/A — no visual rendering change.