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/app.module.ts

@@ -15,7 +15,7 @@ import { LayoutsModule } from "./layouts/layouts.module";
 import { KnowledgeModule } from "./knowledge/knowledge.module";
 import { UsersModule } from "./users/users.module";
 import { WebSocketModule } from "./websocket/websocket.module";
-import { OllamaModule } from "./ollama/ollama.module";
+import { LlmModule } from "./llm/llm.module";
 
 @Module({
   imports: [
@@ -33,7 +33,7 @@ import { OllamaModule } from "./ollama/ollama.module";
     KnowledgeModule,
     UsersModule,
     WebSocketModule,
-    OllamaModule,
+    LlmModule,
   ],
   controllers: [AppController],
   providers: [AppService],