[Contracts] Add content appeal and reinstatement

[Kaylahray]

Description

Content can be flagged and auto-suspended, but there is no structured on-chain appeal flow to restore content after moderation review.

User Story

As a user,
I want to appeal a moderation suspension,
so that valid content can be restored when the review was incorrect.

Requirements and Context

• Files: contracts/geev-core/src/governance.rs, contracts/geev-core/src/admin.rs, contracts/geev-core/src/test.rs
• Add an appeal state and a reinstatement action
• Restrict appeal resolution to admin or moderator authority
• Preserve the original flag count and moderation history for auditability

Suggested Implementation

// APPEAL FLOW
// 1. Mark a flagged item as under appeal.
// 2. Allow an admin to restore the item or keep it suspended.
// 3. Keep the flag and moderation history intact.
// 4. Emit appeal resolution events.

Acceptance Criteria

• Suspended content can enter an appeal state.
• Admins can reinstate content after review.
• Moderation history is preserved for audit purposes.

Submission Guidelines

• Branch: feat/content-appeals
• Depends on: content flagging and suspension logic
• PR: feat(contracts): add moderation appeal and reinstatement flow

[TEEZY234]

@TEEZY234 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I’d like to work on this issue.

I have experience building Soroban smart contract governance and moderation flows and will implement a structured appeal and reinstatement system for flagged content. I will extend the existing moderation logic to introduce an appeal state that allows suspended content to be reviewed without losing its original audit history.

My implementation will ensure that appeals can be initiated for suspended content, reviewed only by authorized admin or moderator roles, and resolved either by reinstating or maintaining the suspension. I will also ensure that all flagging and moderation history remains intact for full auditability and transparency.

Additionally, I will add proper event emissions for appeal resolution and comprehensive tests covering appeal initiation, admin reinstatement, and state preservation scenarios

ℹ️ Repo Maintainers: To accept this application, review their application or assign @TEEZY234 to this issue.