♻️(frontend) reorganize starting frontend code

- we now have "features" to try to organize code by intent instead of
code type. everything at the root of frontend, not in feature/, is
global
- customized the panda config a bunch to try to begin to have an actual
design system. The idea is to prevent using arbitrary values here and
there in the code, but rather semantic tokens
- changed the userAuth code logic to handle the fact that a 401 on the
users/me call is not really an error per say, but rather an indication
the user is not logged in

src/frontend/src/features/auth/api/fetchUser.ts

@@ -0,0 +1,25 @@
+import { ApiError } from '@/api/ApiError'
+import { fetchApi } from '@/api/fetchApi'
+import { type ApiUser } from './ApiUser'
+
+/**
+ * fetch the logged in user from the api.
+ *
+ * If the user is not logged in, the api returns a 401 error.
+ * Here our wrapper just returns false in that case, without triggering an error:
+ * this is done to prevent unnecessary query retries with react query
+ */
+export const fetchUser = (): Promise<ApiUser | false> => {
+  return new Promise((resolve, reject) => {
+    fetchApi<ApiUser>('/users/me')
+      .then(resolve)
+      .catch((error) => {
+        // we assume that a 401 means the user is not logged in
+        if (error instanceof ApiError && error.statusCode === 401) {
+          resolve(false)
+        } else {
+          reject(error)
+        }
+      })
+  })
+}