✨ 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/api-keys/api-keys.controller.ts

@@ -0,0 +1,97 @@
+import {
+	Controller,
+	Get,
+	Post,
+	Patch,
+	Delete,
+	Body,
+	Param,
+	Query,
+	UseGuards,
+} from '@nestjs/common';
+import { JwtAuthGuard, CurrentUser, CurrentUserData } from '@manacore/shared-nestjs-auth';
+import { ApiKeysService } from './api-keys.service';
+import { CreateApiKeyDto, UpdateApiKeyDto } from './dto';
+import { UsageService } from '../usage/usage.service';
+
+@Controller('api-keys')
+@UseGuards(JwtAuthGuard)
+export class ApiKeysController {
+	constructor(
+		private readonly apiKeyService: ApiKeysService,
+		private readonly usageService: UsageService
+	) {}
+
+	@Post()
+	async create(@CurrentUser() user: CurrentUserData, @Body() dto: CreateApiKeyDto) {
+		const result = await this.apiKeyService.create(user.userId, dto);
+		return {
+			message: 'API key created successfully. Save your key - it will not be shown again.',
+			key: result.key,
+			apiKey: result.apiKey,
+		};
+	}
+
+	@Get()
+	async list(@CurrentUser() user: CurrentUserData) {
+		const keys = await this.apiKeyService.listByUser(user.userId);
+		return { apiKeys: keys };
+	}
+
+	@Get(':id')
+	async get(@CurrentUser() user: CurrentUserData, @Param('id') id: string) {
+		const key = await this.apiKeyService.getByIdAndUser(id, user.userId);
+		return { apiKey: key };
+	}
+
+	@Patch(':id')
+	async update(
+		@CurrentUser() user: CurrentUserData,
+		@Param('id') id: string,
+		@Body() dto: UpdateApiKeyDto
+	) {
+		const key = await this.apiKeyService.update(id, user.userId, dto);
+		return { apiKey: key };
+	}
+
+	@Delete(':id')
+	async delete(@CurrentUser() user: CurrentUserData, @Param('id') id: string) {
+		await this.apiKeyService.delete(id, user.userId);
+		return { message: 'API key deleted successfully' };
+	}
+
+	@Post(':id/regenerate')
+	async regenerate(@CurrentUser() user: CurrentUserData, @Param('id') id: string) {
+		const result = await this.apiKeyService.regenerate(id, user.userId);
+		return {
+			message: 'API key regenerated successfully. Save your new key - it will not be shown again.',
+			key: result.key,
+			apiKey: result.apiKey,
+		};
+	}
+
+	@Get(':id/usage')
+	async getUsage(
+		@CurrentUser() user: CurrentUserData,
+		@Param('id') id: string,
+		@Query('days') days?: string
+	) {
+		// Verify ownership
+		await this.apiKeyService.getByIdAndUser(id, user.userId);
+
+		const daysNum = parseInt(days || '30', 10);
+		const usage = await this.usageService.getDailyUsage(id, daysNum);
+
+		return { usage };
+	}
+
+	@Get(':id/usage/summary')
+	async getUsageSummary(@CurrentUser() user: CurrentUserData, @Param('id') id: string) {
+		// Verify ownership
+		await this.apiKeyService.getByIdAndUser(id, user.userId);
+
+		const summary = await this.usageService.getUsageSummary(id);
+
+		return { summary };
+	}
+}