✨ feat: add mana-api-gateway for monetizing core services

Implement custom NestJS API Gateway for mana-search, mana-stt, and mana-tts:

- API Key management with CRUD operations and key regeneration
- Redis-based sliding window rate limiting
- Credit-based billing with tier support (free, pro, enterprise)
- Usage tracking with daily aggregates
- Proxy services to backend microservices
- Prometheus metrics endpoint
- JWT auth for management API, API key auth for public API

Database schema uses separate `api_gateway` schema in shared manacore DB.

services/mana-api-gateway/src/proxy/proxy.module.ts

@@ -0,0 +1,56 @@
+import { Module } from '@nestjs/common';
+import { MulterModule } from '@nestjs/platform-express';
+import { memoryStorage } from 'multer';
+import { ConfigService } from '@nestjs/config';
+import Redis from 'ioredis';
+import { ProxyController } from './proxy.controller';
+import { SearchProxyService, SttProxyService, TtsProxyService } from './services';
+import { ApiKeysModule } from '../api-keys/api-keys.module';
+import { UsageModule } from '../usage/usage.module';
+import { CreditsModule } from '../credits/credits.module';
+import { ApiKeyGuard } from '../guards/api-key.guard';
+import { RateLimitGuard, REDIS_CLIENT } from '../guards/rate-limit.guard';
+import { CreditsGuard } from '../guards/credits.guard';
+import { UsageTrackingInterceptor } from '../common/interceptors/usage-tracking.interceptor';
+
+@Module({
+	imports: [
+		MulterModule.register({
+			storage: memoryStorage(),
+			limits: {
+				fileSize: 100 * 1024 * 1024, // 100MB max file size
+			},
+		}),
+		ApiKeysModule,
+		UsageModule,
+		CreditsModule,
+	],
+	controllers: [ProxyController],
+	providers: [
+		SearchProxyService,
+		SttProxyService,
+		TtsProxyService,
+		ApiKeyGuard,
+		RateLimitGuard,
+		CreditsGuard,
+		UsageTrackingInterceptor,
+		{
+			provide: REDIS_CLIENT,
+			useFactory: (configService: ConfigService) => {
+				const host = configService.get<string>('redis.host') || 'localhost';
+				const port = configService.get<number>('redis.port') || 6379;
+				const password = configService.get<string>('redis.password');
+
+				return new Redis({
+					host,
+					port,
+					password: password || undefined,
+					keyPrefix: configService.get<string>('redis.keyPrefix') || 'api-gateway:',
+				});
+			},
+			inject: [ConfigService],
+		},
+	],
+	exports: [REDIS_CLIENT],
+})
+export class ProxyModule {}