chore: setup design references

docs/design/emails.md

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+# Emails
+
+Go `html/template` files, ready to replace `internal/infrastructure/mailer/templates/`:
+
+- `source/emails/verification.html` uses `{{.Host}}` and `{{.VerificationCode}}`, linking to `{{.Host}}/register/validate?c={{.VerificationCode}}`.
+- `source/emails/password-reset.html` uses `{{.Host}}`, `{{.VerificationCode}}` and `{{.Email}}`, linking to `{{.Host}}/register/reset/validate?c={{.VerificationCode}}&email={{.Email}}`.
+
+Previews: `source/RenewCMS Emails.dc.html`.
+
+## Transactional emails
+
+Two Go html/template files: emails/verification.html and emails/password-reset.html . They use a table layout with inline CSS and a 600 px maximum width. The button is bulletproof: a colored table cell plus a padded link, so it survives Outlook. Each has a plain-URL fallback, a hidden preheader, and prefers-color-scheme overrides for clients that support them. The mark is live text in a black cell rather than an image, so it shows even when images are blocked. Previews below use example values.
+
+Suggested subjects are "Verify your RenewCMS account" and "Reset your RenewCMS password". html/template escapes the .Email value for the query string in the reset link (the @ becomes %40), and the confirm route reads it back decoded.