Adds lib/mailer.ts (sendeKontaktEmail, MBO-Tech-IT branding),
lib/email-queue.ts (Supabase-fallback, graceful no-op when not configured),
lib/supabase.ts (stub for later integration), admin API routes for
SMTP-test and queue management, and instrumentation.ts for the queue worker.
Excludes modules/ from TypeScript compilation.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
