Contest-scoped problem access #512
Description
This feature request proposes exposing /contest/{key}/{order} to directly present instances of ContestProblem.
In the current design, when a user accesses a problem via /problem/{code}/, the backend checks profile.current_contest to determine whether the problem belongs to a contest the user is currently participating in. When a user switches between contests, access to the same problem depends on whether profile.current_contest matches the target contest, forcing the user to repeatedly rejoin contests. This results in poor UX.
This proposal makes ContestProblem a first-class entity rather than a mere many-to-many relationship, allowing contest-scoped problem access.