feat(#21): implement ollama integration

- Add Ollama client library (ollama npm package)
- Create LlmService for chat completion and embeddings
- Support streaming responses via Server-Sent Events
- Add configuration via env vars (OLLAMA_HOST, OLLAMA_TIMEOUT)
- Create endpoints: GET /llm/health, GET /llm/models, POST /llm/chat, POST /llm/embed
- Replace old OllamaModule with new LlmModule
- Add comprehensive tests with >85% coverage

Closes #21

apps/api/src/llm/llm.module.ts

@@ -0,0 +1,5 @@
+import { Module } from "@nestjs/common";
+import { LlmController } from "./llm.controller";
+import { LlmService } from "./llm.service";
+@Module({ controllers: [LlmController], providers: [LlmService], exports: [LlmService] })
+export class LlmModule {}