feat: migrate AI to Vercel AI SDK, add OpenAI provider, fix worklist

- Replace raw @anthropic-ai/sdk with Vercel AI SDK (generateText, tool, generateObject)
- Add provider abstraction (ai-provider.ts) — swap OpenAI/Anthropic via env var
- AI chat controller: dynamic KB from platform (clinics, packages, insurance), zero hardcoding
- AI enrichment service: use generateObject with Zod schema instead of manual JSON parsing
- Worklist: resolve agent name from platform currentUser API instead of JWT decode
- Worklist: fix GraphQL field names to match platform remapping (source, status, direction, etc.)
- Config: add AI_PROVIDER, AI_MODEL, OPENAI_API_KEY env vars

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ai/ai.module.ts

@@ -1,8 +1,10 @@
 import { Module } from '@nestjs/common';
+import { PlatformModule } from '../platform/platform.module';
 import { AiEnrichmentService } from './ai-enrichment.service';
 import { AiChatController } from './ai-chat.controller';
 
 @Module({
+    imports: [PlatformModule],
     controllers: [AiChatController],
     providers: [AiEnrichmentService],
     exports: [AiEnrichmentService],