Covers dev (Mailpit), production SMTP, all env vars with defaults,
common provider settings, and how to disable mail entirely.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Missing closing braces caused Spring to inject the literal placeholder
string instead of resolving the property, silently ignoring any
app.admin.username / app.admin.password env-var overrides.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
