Set up sign in and sign up

[SantaClaas]

Sign in flow is now:

---
title: "Sign in flow: The happy path"
---

flowchart LR
    A[Sign up page] --> B[Enter email & name] --> C[Open link in email] --> D[Signed in]
    E[Sign in page] --> F[Enter email] --> C

Other changes:

• Added nanoid for better non-guessable ids that don't leak internal information such as count of users
• Added ability to extract authenticated user information in request handlers to fetch user related data (e.g. a user's surveys)
• ...and things I probably forgot to mention so please ask if there's any question

Not implemented:

• Refresh session to keep users signed in as long as they are active and therefore reduce friction
• Passkey support for less sign in steps/friction

I know this is a lot so we can go through it later if you want.

[SantaClaas]

Forgot to mention: I've used Resend for sending emails because it was the easiest way. We could later add SMTP so users can use a private email account they have as an alternative.

[SantaClaas]

Also missing: Sign out button to delete cookie and invalidate session

[SantaClaas]

Also missing: redirect user when signed in and trying to sign in again