Add OpenAI-compatible LLM client service (v0.19.0)

LlmService wraps the local OpenAI-compatible server (default
http://192.168.1.70:1111/v1, no auth) with native fetch only — no new
dependencies. listModels() -> data[].id; chat(messages, opts?) ->
choices[0].message.content (non-2xx throws with status + body snippet);
summarize(text) = chat() with a concise-summary system prompt.

Env: LLM_API_BASE / LLM_MODEL (qwen3.8-27b) / LLM_TIMEOUT_MS (60000,
AbortSignal.timeout). Plain feature module wired into app.module.ts;
docs synced (AGENTS.md, README env list).

src/llm/llm.module.ts

@@ -0,0 +1,8 @@
+import { Module } from '@nestjs/common';
+import { LlmService } from './llm.service.js';
+
+@Module({
+  providers: [LlmService],
+  exports: [LlmService],
+})
+export class LlmModule {}