Roadmap: Merging all Client apps into a single project

We would like to reduce the spread of the project to have to maintain and work on a single app for the client.

### Project preparation:
- [x] move to `pnpm` for package management: lighter and faster than `yarn` and also supports workspaces (will be useful in the future maybe) #211
- Progressively update the configurations of the project to prepare it
- [x] update tsconfig to use up-to-date config from vite templates #376
- [x] update eslint config to use flatconfig and v9 #377

### Migration to `@tanstack/react-router:
Use `@tanstack/react-router` instead of `react-router-dom` as it allows to split on routes and managing routes with typesafety is awesome.
- Migrate account to `@tanstack/react-router`
- [x] Setup account pages with the new router
- [x] Keep redirections to auth.graasp.org
- Migrate Landing page here
- [x] create all the pages needed for landing here
- [x] Figure out multi-lang support with urls
- [x] Deploy to `graasp.org` instead of `account.graasp.org`
- [ ] #481

### Making the project single origin
We want to host the project on a single domain, to:
- simplify cookie management and make it more secure, no more (.graasp.org cookies)
- remove the need for CORS
- streamline the devlopment and usage of common layouts in a single project

- Backend should be reachable at `graasp.org/api`
- [ ] Infra: update load-balancer config to serve `/api` requests to the backend
- [ ] remove the need for API_HOST in query-client, just use relative routes
- [x] migrate player here
- [x] migrate analytics here
- [x] migrate builder here
- [x] `builder.graasp.org`, `auth.graasp.org`, `player.graasp.org` should redirect to the path equivalents using the load-balancer
- [ ] library should be served on a subpath too
- [ ] We should be able to remove the CORS for the core endpoints since all the trafic should be from the `graasp.org` domain.