Move to tanstack router

[anthony2261]

Closes #236 <3

[RamiAwar]

Other comments:

• Didn't see any changes relating to the landing page metadata, which was the whole point of this rewrite. Did I miss this maybe? Do we now support dynamic metadata on the landing pages?

• Are we still separating landing / app? Or is landing accessible from app? This separation is not clear to me anymore, didn't notice it when scrolling through the changes

[anthony2261]

@RamiAwar

Didn't see any changes relating to the landing page metadata, which was the whole point of this rewrite.

Better not to mix moving to tanstack and messing around with context in the same PR, we can do this next

Are we still separating landing / app?

Yes, see code inside src/routes/__root.tsx, src/routes/_app.tsx and frontend/src/routes/_landing.tsx

Clarification: The code inside _app.tsx runs whenever any path inside _app/ is reached, eg. /_app/user (_app is not actually shown in the URL, but tells the code which logical path it falls under). So, if you open the /user endpoint, the code will run the beforeLoad method inside _app.tsx, and redirect you to / if NODE_ENV is not local

[anthony2261]

I need to test that auth works. Might need to make a small addition to beforeLoad