feat(governance): add appeal and review flow for auto-suspended content

[Birdmannn]

Description

feat(governance): appeal & restore workflow for suspended content

Closes #412

What

Adds a documented recovery path for content that was auto-suspended by coordinated or mistaken flagging.

Changes

governance.rs

• file_appeal(user, target_id) — creator-only entrypoint that transitions Suspended → UnderAppeal for both Giveaways and HelpRequests. Emits ContentAppealed.

admin.rs

• resolve_appeal(target_id, restore) — admin-only entrypoint. restore=true returns content to Active/Open; restore=false confirms the suspension. Emits AppealResolved.

types.rs

• GiveawayStatus::UnderAppeal and HelpRequestStatus::UnderAppeal variants (already present, wired up by the above).

test.rs

12 new governance tests covering the full appeal lifecycle, plus a fix for a pre-existing HelpRequest struct initializer missing created_at / expires_at.

Policy

Rule	Behaviour
Who can appeal	Content creator only (NotCreator otherwise)
Valid appeal window	Content must be Suspended (InvalidStatus otherwise)
Who can resolve	Admin only (panics for anyone else)
Flag history on restore	Preserved — count is not reset, preventing immediate re-suspension from the same flaggers
Re-suspension after restore	Allowed — fresh unique flaggers can still reach the threshold

Tests (97 passing, 0 failing)

• Creator appeal transitions status to UnderAppeal (Giveaway + HelpRequest)
• Non-creator appeal returns NotCreator
• Appeal on non-suspended content returns InvalidStatus
• Admin restore sets status back to Active / Open
• Admin denial keeps status Suspended
• Unauthorized resolve_appeal panics
• Flag count is preserved after restore
• Restored content can be re-suspended by new unique flaggers
• ContentAppealed and AppealResolved events are emitted

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Checklist

• I have tested my changes locally
• I have updated documentation as needed
• I have run npx prisma generate after schema changes
• I have run npx prisma migrate dev or npx prisma migrate deploy as appropriate

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Post-Merge Steps for Maintainers

If this PR includes changes to the Prisma schema:

1. Run the following command to apply the migration to your database:

   npx prisma migrate deploy

   or, for local development:

   npx prisma migrate dev

2. Ensure your CI pipeline runs the migration before tests (add this step if missing):

   - name: Run Prisma Migrate
     run: npx prisma migrate deploy

3. Make sure the database user in CI has permission to run migrations.

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If you have any questions, please comment on this PR.