[api] Register SearchModule, TokensModule, and StatsModule in AppModule

[Mimah97]

Problem

Three fully implemented NestJS modules exist but are not imported in apps/api/src/app.module.ts:

• SearchModule → /search returns 404
• TokensModule → /tokens unreachable; TokenEnrichmentService.onModuleInit() never starts
• StatsModule → StatsWorker and StatsScheduler never run; pool TVL/volume24h/feeApr stay stale

Acceptance criteria

• Import SearchModule, TokensModule, and StatsModule in AppModule
• GET /search?q=USDC returns search results
• GET /tokens returns enriched token metadata
• Pool stats update on schedule via StatsScheduler

Files

• apps/api/src/app.module.ts