The Docker runtime image only ships dist/, but mail-config.service.ts
pointed at src/mail/mail-templates and nest-cli.json never copied the
.hbs files into dist/ either. This was silently masked before because
the return-before-sendMail bug meant the path was never touched; fixing
that bug now surfaces it as a hard crash on boot (readFileSync throwing
synchronously inside the MailerModule factory). Resolve the templates
dir from __dirname instead, which is correct in both dev (src/mail) and
the compiled image (dist/mail), and add the mail-templates .hbs files
to nest-cli.json's asset copy list so they actually land in dist/.
