feature request: Headless API support

### What problem did you meet? Hi, I haven't been able to find an optimal solution for creating a custom authorization form the way I'm used to with other providers like WorkOS, Ory Kratos. ### Describe what you'd like Logto to have It would be great to have a headless API for login. This is important because styling, static asset loading optimization, display mode (modal vs. dedicated page), loading strategy, PoW captcha (like ALTCHA), and form fields often don't align with a pre-built solution. Even registration via a one-time code feels unusual, but that's exactly the flow many of us expected. Could you please let me know if there are any plans to implement this?