Separate OIDC discovery endpoint into its own blueprint registered at
root level (required by OIDC spec for .well-known path). Move all other
OIDC endpoints to /api/v1/oidc to conform to API versioning standard.
BREAKING CHANGE: OIDC endpoint URLs changed from /oidc/* to /api/v1/oidc/*
Add pluggable email provider system supporting SMTP, Mailgun, and SendGrid
with factory pattern for runtime provider selection. Includes branded HTML
email templates for verification, password reset, MFA notifications, and
organization invites.
Also rebrands all email content from Gatehouse to Secuird, adds email
provider configuration options, and fixes duplicate log handlers in
development mode.