fix: register mail layout partial on handlebars singleton for real mailer wiring

The HandlebarsAdapter reads partials config from a top-level sibling of
`template` (mailerOptions.options.partials), not from
template.options.partials where it was nested. Because the mail templates
use partial blocks ({{#> layout}}...{{/layout}}), the unregistered partial
rendered silently as an unstyled fragment instead of throwing, so this went
unnoticed. A config-only fix also breaks on Windows because the adapter's
glob-based directory loader mishandles backslash path separators.

Fix registers the shared `layout` partial directly on the handlebars module
singleton in MailConfigService, bypassing the broken glob loader entirely.

Also:
- add mail-config.service.spec.ts, an integration test that drives the real
  MailerOptions + HandlebarsAdapter wiring (would have caught this bug,
  unlike the existing template-only spec which registers the partial itself)
- remove stale nestjs-i18n references from .env.example, env-example, and
  the backend README (i18n was already removed from the code)
- add missing trailing newlines to activation.hbs and reset-password.hbs

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.example

@@ -2,8 +2,6 @@ NODE_ENV=production
 APP_PORT=3999
 APP_NAME="NestJS API"
 API_PREFIX=api
-APP_FALLBACK_LANGUAGE=en
-APP_HEADER_LANGUAGE=x-custom-lang
 FRONTEND_DOMAIN=http://localhost:3999
 BACKEND_DOMAIN=http://localhost:3999
 

env-example

@@ -2,8 +2,6 @@ NODE_ENV=development
 APP_PORT=3000
 APP_NAME="NestJS API"
 API_PREFIX=api
-APP_FALLBACK_LANGUAGE=en
-APP_HEADER_LANGUAGE=x-custom-lang
 FRONTEND_DOMAIN=http://localhost:3000
 BACKEND_DOMAIN=http://localhost:3000
 

myteamwallet_backend/README.md

@@ -26,7 +26,6 @@ Seeden: npm run seed:run
 - [x] Sign in and sign up via email.
 - [x] Social sign in (Apple, Facebook, Google, Twitter).
 - [x] Admin and User roles.
-- [x] I18N ([nestjs-i18n](https://www.npmjs.com/package/nestjs-i18n)).
 - [x] File uploads. Support local and Amazon S3 drivers.
 - [x] Swagger.
 - [x] E2E and units tests.

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

@@ -0,0 +1,56 @@
+import * as path from 'path';
+import { ConfigService } from '@nestjs/config';
+import { MailConfigService } from './mail-config.service';
+
+describe('MailConfigService integration', () => {
+  it('produces mailer options whose adapter actually renders the shared layout partial', (done) => {
+    const workingDirectory = path.join(__dirname, '..', '..');
+    const configValues: Record<string, unknown> = {
+      'app.workingDirectory': workingDirectory,
+      'mail.host': 'localhost',
+      'mail.port': 1025,
+      'mail.ignoreTLS': true,
+      'mail.secure': false,
+      'mail.requireTLS': false,
+      'mail.user': '',
+      'mail.password': '',
+      'mail.defaultName': 'TeamWallet',
+      'mail.defaultEmail': 'test@example.com',
+    };
+    const configService = {
+      get: (key: string) => configValues[key],
+    } as unknown as ConfigService;
+
+    const options = new MailConfigService(configService).createMailerOptions();
+
+    const mail: {
+      data: {
+        template: string;
+        context: Record<string, unknown>;
+        html?: string;
+      };
+    } = {
+      data: {
+        template: 'activation',
+        context: {
+          title: 'Test',
+          year: 2026,
+          firstName: 'Max',
+          url: 'https://example.com/confirm-email/abc',
+          actionTitle: 'Jetzt bestätigen',
+        },
+      },
+    };
+
+    options.template.adapter.compile(
+      mail,
+      (err?: Error) => {
+        expect(err).toBeUndefined();
+        expect(mail.data.html).toContain('TeamWallet');
+        expect(mail.data.html).toContain('tw-wordmark');
+        done();
+      },
+      options,
+    );
+  });
+});

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

@@ -1,4 +1,6 @@
 import * as path from 'path';
+import * as fs from 'fs';
+import * as handlebars from 'handlebars';
 import { Injectable } from '@nestjs/common';
 import { ConfigService } from '@nestjs/config';
 import { MailerOptions, MailerOptionsFactory } from '@nestjs-modules/mailer';
@@ -9,6 +11,21 @@ export class MailConfigService implements MailerOptionsFactory {
   constructor(private configService: ConfigService) {}
 
   createMailerOptions(): MailerOptions {
+    const templatesDir = path.join(
+      this.configService.get('app.workingDirectory'),
+      'src',
+      'mail',
+      'mail-templates',
+    );
+
+    handlebars.registerPartial(
+      'layout',
+      fs.readFileSync(
+        path.join(templatesDir, 'partials', 'layout.hbs'),
+        'utf-8',
+      ),
+    );
+
     return {
       transport: {
         host: this.configService.get('mail.host'),
@@ -27,24 +44,10 @@ export class MailConfigService implements MailerOptionsFactory {
         )}" <${this.configService.get('mail.defaultEmail')}>`,
       },
       template: {
-        dir: path.join(
-          this.configService.get('app.workingDirectory'),
-          'src',
-          'mail',
-          'mail-templates',
-        ),
+        dir: templatesDir,
         adapter: new HandlebarsAdapter(),
         options: {
           strict: true,
-          partials: {
-            dir: path.join(
-              this.configService.get('app.workingDirectory'),
-              'src',
-              'mail',
-              'mail-templates',
-              'partials',
-            ),
-          },
         },
       },
     } as MailerOptions;