fix(mail): resolve templates from __dirname so they exist in the built image

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/.

myteamwallet_backend/src/mail/mail-config.service.ts

@@ -11,12 +11,10 @@ export class MailConfigService implements MailerOptionsFactory {
   constructor(private configService: ConfigService) {}
 
   createMailerOptions(): MailerOptions {
-    const templatesDir = path.join(
-      this.configService.get('app.workingDirectory'),
-      'src',
-      'mail',
-      'mail-templates',
-    );
+    // __dirname resolves to src/mail in dev (ts-node) and dist/mail in the
+    // built image, so this stays correct without depending on whether the
+    // process was started from a source or compiled checkout.
+    const templatesDir = path.join(__dirname, 'mail-templates');
 
     handlebars.registerPartial(
       'layout',