feat(api): conversations + messages routes

Add conversations CRUD-lite (list, create, get, PATCH status, PATCH
summary which flips status to summarized) and conversation-scoped
messages (append, list ordered by created_at).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/api/conversations.test.js

@@ -0,0 +1,41 @@
+import { describe, it, expect, beforeAll } from 'vitest';
+import request from 'supertest';
+import { setup } from './helpers.js';
+
+let app, ownerHeaders;
+beforeAll(async () => { ({ app, ownerHeaders } = await setup()); });
+
+describe('conversations + messages routes', () => {
+  it('POST creates and GET returns', async () => {
+    const c = await request(app).post('/api/conversations').set(ownerHeaders)
+      .send({ title: 'chat' });
+    expect(c.status).toBe(201);
+    const get = await request(app).get(`/api/conversations/${c.body.id}`).set(ownerHeaders);
+    expect(get.body.id).toBe(c.body.id);
+  });
+
+  it('append + list messages in order', async () => {
+    const c = await request(app).post('/api/conversations').set(ownerHeaders).send({});
+    await request(app).post(`/api/conversations/${c.body.id}/messages`).set(ownerHeaders)
+      .send({ role: 'user', body: 'one' });
+    await request(app).post(`/api/conversations/${c.body.id}/messages`).set(ownerHeaders)
+      .send({ role: 'assistant', body: 'two' });
+    const list = await request(app).get(`/api/conversations/${c.body.id}/messages`).set(ownerHeaders);
+    expect(list.body.map(m => m.body)).toEqual(['one', 'two']);
+  });
+
+  it('PATCH /:id/summary flips status to summarized', async () => {
+    const c = await request(app).post('/api/conversations').set(ownerHeaders).send({});
+    const res = await request(app).patch(`/api/conversations/${c.body.id}/summary`).set(ownerHeaders)
+      .send({ summary: 'tldr' });
+    expect(res.body.status).toBe('summarized');
+    expect(res.body.summary).toBe('tldr');
+  });
+
+  it('append on missing conv → 404', async () => {
+    const res = await request(app)
+      .post('/api/conversations/00000000-0000-0000-0000-000000000000/messages').set(ownerHeaders)
+      .send({ role: 'user', body: 'x' });
+    expect(res.status).toBe(404);
+  });
+});