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.service.spec.ts

@@ -0,0 +1,104 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import type { ChatMessage } from './llm.service.js';
+import { LlmService } from './llm.service.js';
+
+const BASE = 'http://192.168.1.70:1111/v1';
+
+function json(body: unknown): Response {
+  return { ok: true, status: 200, json: async () => body } as Response;
+}
+
+/** Fresh service with a clean env (explicit base/model/timeout). */
+function makeService(): LlmService {
+  process.env.LLM_API_BASE = BASE;
+  process.env.LLM_MODEL = 'qwen3.8-27b';
+  process.env.LLM_TIMEOUT_MS = '60000';
+  return new LlmService();
+}
+
+describe('LlmService', () => {
+  let fetchMock: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    fetchMock = vi.fn();
+    vi.stubGlobal('fetch', fetchMock);
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    for (const k of ['LLM_API_BASE', 'LLM_MODEL', 'LLM_TIMEOUT_MS'])
+      delete process.env[k];
+  });
+
+  it('listModels returns the data[].id strings from GET /models', async () => {
+    const svc = makeService();
+    fetchMock.mockResolvedValueOnce(
+      json({
+        data: [
+          { id: 'qwen3.8-27b' },
+          { id: 'text-embedding-nomic-embed-text-v1.5' },
+        ],
+      }),
+    );
+
+    await expect(svc.listModels()).resolves.toEqual([
+      'qwen3.8-27b',
+      'text-embedding-nomic-embed-text-v1.5',
+    ]);
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    expect(fetchMock.mock.calls[0][0]).toBe(`${BASE}/models`);
+  });
+
+  it('chat posts model+messages and returns choices[0].message.content', async () => {
+    const svc = makeService();
+    fetchMock.mockResolvedValueOnce(
+      json({ choices: [{ message: { content: 'hello back' } }] }),
+    );
+
+    const messages: ChatMessage[] = [
+      { role: 'system', content: 'be brief' },
+      { role: 'user', content: 'hi' },
+    ];
+    await expect(
+      svc.chat(messages, { maxTokens: 50, temperature: 0.2 }),
+    ).resolves.toBe('hello back');
+
+    const [url, init] = fetchMock.mock.calls[0];
+    expect(url).toBe(`${BASE}/chat/completions`);
+    expect(init.method).toBe('POST');
+    expect(JSON.parse(init.body)).toEqual({
+      model: 'qwen3.8-27b',
+      messages,
+      maxTokens: 50,
+      temperature: 0.2,
+    });
+  });
+
+  it('chat throws on non-2xx with the HTTP status in the message', async () => {
+    const svc = makeService();
+    fetchMock.mockResolvedValueOnce({
+      ok: false,
+      status: 503,
+      text: async () => 'upstream down',
+    } as Response);
+
+    await expect(svc.chat([{ role: 'user', content: 'hi' }])).rejects.toThrow(
+      /HTTP 503.*upstream down/,
+    );
+  });
+
+  it('summarize calls chat with the system prompt plus the user text', async () => {
+    const svc = makeService();
+    fetchMock.mockResolvedValueOnce(
+      json({ choices: [{ message: { content: 'the summary' } }] }),
+    );
+
+    await expect(svc.summarize('a long text')).resolves.toBe('the summary');
+
+    const [, init] = fetchMock.mock.calls[0];
+    expect(JSON.parse(init.body).messages).toEqual([
+      { role: 'system', content: 'Summarize the following text concisely.' },
+      { role: 'user', content: 'a long text' },
+    ]);
+  });
+});