Prefill admin email and make it mandatory

[bcotrim]

Related issues

Related to #2527 (Add support for Blueprints login)

Proposed Changes

• Prefill the admin email field with admin@localhost.com instead of leaving it empty
• Make email validation mandatory (always enabled, not conditional on user input)
• Remove the informational comment explaining the default value
• For pre-existing sites without a stored email, automatically fetch it from WordPress via wp user get <username> --field=user_email when opening site settings (uses the stored admin username or defaults to admin)
• Simplify form submission logic to always send the email value (since it's now always populated)

Testing Instructions

For new sites:

1. Create a new site
2. In the advanced settings, verify the email field is prefilled with admin@localhost.com
3. Try to clear the field and save — should show validation error "Admin email cannot be empty."
4. Enter a valid email and confirm the site is created

For pre-existing sites:

1. If you have a site created before PR Add support for Blueprints login #2527 without stored email:
   • Open its settings
   • Watch the email field populate with the real email from WordPress (fetched via WP-CLI)
2. Edit the email and save — should persist to appdata

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 60442fa vs trunk

site-editor

Metric	trunk	60442fa	Diff	Change
load	1507.00 ms	1445.00 ms	-62.00 ms	🟢 -4.1%

site-startup

Metric	trunk	60442fa	Diff	Change
siteCreation	7080.00 ms	7111.00 ms	+31.00 ms	⚪ 0.0%
siteStartup	4932.00 ms	4944.00 ms	+12.00 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[gcsecsey]

Thanks @bcotrim for improving this! 🙌 This is looking good to me, and tests well. Unfortunately I didn't have a site from earlier, but I confirm the validation works great for a new site:

CleanShot.2026-02-27.at.15.26.39.mp4

[epeicher]

Thanks @bcotrim! I have tested it, and I see the email validation when creating the site and when deleting the email from an existing (or new) site. LGTM!

One small detail that can be tacked as a follow-up is that the validation message displayed when editing a site and deleting the email is hidden from the viewport and the user needs to scroll down. Initially, I saw the red outline but didn't see the message, then I realised I needed to scroll, please see the video below

CleanShot.2026-02-27.at.17.49.57.mp4

This is such a minor detail, but I believe addressing it will enhance the validation UX.