✨ 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.controller.ts

@@ -0,0 +1,103 @@
+import {
+	Controller,
+	Post,
+	Get,
+	Body,
+	UseGuards,
+	UseInterceptors,
+	UploadedFile,
+	Res,
+	Query,
+} from '@nestjs/common';
+import { FileInterceptor } from '@nestjs/platform-express';
+import { Response } from 'express';
+import { ApiKeyGuard } from '../guards/api-key.guard';
+import { RateLimitGuard } from '../guards/rate-limit.guard';
+import { CreditsGuard } from '../guards/credits.guard';
+import { UsageTrackingInterceptor } from '../common/interceptors/usage-tracking.interceptor';
+import { ApiKeyParam } from '../common/decorators/api-key.decorator';
+import { ApiKeyData } from '../api-keys/api-keys.service';
+import {
+	SearchProxyService,
+	SearchRequestDto,
+	ExtractRequestDto,
+	BulkExtractRequestDto,
+} from './services/search-proxy.service';
+import { SttProxyService, TranscribeRequestDto } from './services/stt-proxy.service';
+import { TtsProxyService, SynthesizeRequestDto } from './services/tts-proxy.service';
+
+@Controller('v1')
+@UseGuards(ApiKeyGuard, RateLimitGuard, CreditsGuard)
+@UseInterceptors(UsageTrackingInterceptor)
+export class ProxyController {
+	constructor(
+		private readonly searchProxy: SearchProxyService,
+		private readonly sttProxy: SttProxyService,
+		private readonly ttsProxy: TtsProxyService
+	) {}
+
+	// === SEARCH ===
+
+	@Post('search')
+	async search(@Body() body: SearchRequestDto, @ApiKeyParam() apiKey: ApiKeyData) {
+		return this.searchProxy.search(body);
+	}
+
+	@Get('search/engines')
+	async getEngines() {
+		return this.searchProxy.getEngines();
+	}
+
+	@Post('extract')
+	async extract(@Body() body: ExtractRequestDto) {
+		return this.searchProxy.extract(body);
+	}
+
+	@Post('extract/bulk')
+	async bulkExtract(@Body() body: BulkExtractRequestDto) {
+		return this.searchProxy.bulkExtract(body);
+	}
+
+	// === STT ===
+
+	@Post('stt/transcribe')
+	@UseInterceptors(FileInterceptor('file'))
+	async transcribe(@UploadedFile() file: Express.Multer.File, @Body() body: TranscribeRequestDto) {
+		return this.sttProxy.transcribe(file, body);
+	}
+
+	@Get('stt/models')
+	async getSttModels() {
+		return this.sttProxy.getModels();
+	}
+
+	@Get('stt/languages')
+	async getSttLanguages() {
+		return this.sttProxy.getLanguages();
+	}
+
+	// === TTS ===
+
+	@Post('tts/synthesize')
+	async synthesize(@Body() body: SynthesizeRequestDto, @Res() res: Response) {
+		const audio = await this.ttsProxy.synthesize(body);
+
+		const format = body.format || 'mp3';
+		const contentType =
+			format === 'wav' ? 'audio/wav' : format === 'ogg' ? 'audio/ogg' : 'audio/mpeg';
+
+		res.setHeader('Content-Type', contentType);
+		res.setHeader('Content-Length', audio.length);
+		res.send(audio);
+	}
+
+	@Get('tts/voices')
+	async getTtsVoices() {
+		return this.ttsProxy.getVoices();
+	}
+
+	@Get('tts/languages')
+	async getTtsLanguages() {
+		return this.ttsProxy.getLanguages();
+	}
+}