rate_contribution allows self-rating with no rater identity enforced

[RUKAYAT-CODER]

Background

reputation.rs::rate_contribution updates a content author's contribution_quality running average based on a rating, but the function signature never captures who the rater is:

pub fn rate_contribution(env: &Env, user: Address, rating: u32) {
    assert!(rating <= 5, "Rating must be between 0 and 5");
    let mut reputation = get_reputation(env, &user);
    ...
}

The function's own doc comment admits the gap:

/// # Note
/// The caller is the rater, not the rated user.  The `user` parameter is the
/// content author whose reputation is being updated.  There is currently no
/// check preventing self-rating — this should be enforced at the call site.
///
/// # TODO
/// - Add a `rater: Address` parameter and enforce `rater != user` to prevent
///   self-rating abuse.

Because there's no rater parameter or require_auth-backed identity check at all in this function, any caller can inflate any user's contribution_quality — including their own — with no on-chain record of who submitted the rating and no self-rating guard. This is a direct reputation-manipulation vector, not just a missing nice-to-have.

Implementation Plan

• Add a rater: Address parameter to rate_contribution, call rater.require_auth(), and reject the call (return a validation error) when rater == user.
• Audit call sites of rate_contribution across the contract to pass the correct rater identity.
• Add tests: self-rating is rejected, unauthenticated rating is rejected, and a legitimate third-party rating still updates contribution_quality correctly.

Acceptance Criteria

• rate_contribution requires and authenticates a distinct rater address
• Self-rating (rater == user) is rejected with a clear error
• Tests cover the rejection paths and the happy path