Add application/json+ld content type support

[Copilot]

TinyPEN was rejecting requests with Content-Type: application/json+ld, causing failures for JSON-LD clients.

Changes

• app.js: Configure express.json() to accept both application/json and application/json+ld

  app.use(express.json({ type: ['application/json', 'application/json+ld'] }))

• tests/content-type.test.js: Add test coverage for all endpoints with JSON-LD content type

Original prompt

---

This section details on the original issue you should resolve

<issue_title>application/json+ld</issue_title>
<issue_description>TinyPEN should understand and support this Content-Type.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes application/json+ld #9

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.