add ALTCHA challenge endpoint and env config.

GET /api/altcha/challenge, nullcart-style env validation, and ALTCHA_ENABLED wiring.

backend/src/AppModule.ts

@@ -1,7 +1,9 @@
 import { Module } from '@nestjs/common';
 import { ConfigModule, ConfigService, registerAs } from '@nestjs/config';
 import { TypeOrmModule } from '@nestjs/typeorm';
-import { getAppConfig, getPostgresConfig } from './config';
+import { getAltchaConfig, getAppConfig, getPostgresConfig } from './config';
+import { validate } from './config/validate';
+import { AltchaModule } from './modules/altcha/AltchaModule';
 import { HealthCheckModule } from './modules/healthCheck/HealthCheckModule';
 import { StorageModule } from './modules/storage/StorageModule';
 import { UploadModule } from './modules/upload/UploadModule';
@@ -11,13 +13,19 @@ import { Config } from './types/Config';
     imports: [
         ConfigModule.forRoot({
             isGlobal: true,
-            load: [registerAs('postgres', getPostgresConfig), registerAs('app', getAppConfig)]
+            validate,
+            load: [
+                registerAs('postgres', getPostgresConfig),
+                registerAs('app', getAppConfig),
+                registerAs('altcha', getAltchaConfig)
+            ]
         }),
         TypeOrmModule.forRootAsync({
             useFactory: (configService: ConfigService) => configService.get('postgres') as Config['postgres'],
             inject: [ConfigService]
         }),
         HealthCheckModule,
+        AltchaModule,
         StorageModule,
         UploadModule
     ]