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/dto/embed.dto.ts

@@ -0,0 +1,3 @@
+import { IsArray, IsString, IsOptional } from "class-validator";
+export class EmbedRequestDto { @IsString() model!: string; @IsArray() @IsString({ each: true }) input!: string[]; @IsOptional() @IsString() truncate?: "start" | "end" | "none"; }
+export interface EmbedResponseDto { model: string; embeddings: number[][]; totalDuration?: number; }