feat: Change default registration mode to public

- Updated default REGISTRATION_MODE from 'invite_only' to 'public'
- Applied to both auth.controller.ts and auth.service.ts
- Added REGISTRATION_MODE and REQUIRE_INVITE_CODE to .env file
- System now defaults to open registration unless explicitly configured

Note: Admins can still switch to invite-only mode via the admin
dashboard settings page (functionality to persist settings coming soon).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

maternal-app/maternal-app-backend/src/modules/auth/auth.controller.ts

@@ -52,7 +52,7 @@ export class AuthController {
   @Get('registration/config')
   @HttpCode(HttpStatus.OK)
   async getRegistrationConfig() {
-    const registrationMode = this.configService.get<string>('REGISTRATION_MODE', 'invite_only');
+    const registrationMode = this.configService.get<string>('REGISTRATION_MODE', 'public');
     const requireInviteCode = registrationMode === 'invite_only';
 
     return {

maternal-app/maternal-app-backend/src/modules/auth/auth.service.ts

@@ -55,7 +55,7 @@ export class AuthService {
 
   async register(registerDto: RegisterDto): Promise<AuthResponse> {
     // Check registration mode and validate invite code if required
-    const registrationMode = this.configService.get<string>('REGISTRATION_MODE', 'invite_only');
+    const registrationMode = this.configService.get<string>('REGISTRATION_MODE', 'public');
     const requireInviteCode = registrationMode === 'invite_only';
 
     let validatedInviteCode: InviteCode | null = null;