[Backend] Add content moderation queue with approve/reject workflow

[jobbykings]

Description

As user-generated content (course descriptions, forum posts, assignment submissions) grows, we need a moderation system where flagged or new content can be reviewed, approved, or rejected by moderators before being publicly visible.

Definition of Done

• Content types eligible for moderation: course descriptions, user-submitted resources, discussion posts, reviews
• Auto-flagging based on configurable keyword/pattern blocklist
• User flagging: any authenticated user can "Report" content with a reason
• Moderation queue endpoint: GET /api/admin/moderation/queue with filters by status (pending, approved, rejected), content type, date range
• Moderation actions: approve (content becomes visible), reject with reason (content hidden, author notified), request revision (author can resubmit)
• Moderation history logged in audit trail (see related audit logging issue)
• Author receives notification (in-app + optional email) when content is moderated
• Batch moderation: select multiple items and approve/reject in bulk
• Role-based access: only users with moderator or admin role can access moderation endpoints

Files to Modify

• frontend/src/app/admin/content/moderation/page.tsx
• NEW: backend/src/models/ModerationFlag.ts
• NEW: backend/src/services/moderationService.ts
• NEW: backend/src/routes/admin/moderation.ts
• NEW: backend/src/services/__tests__/moderationService.test.ts
• backend/src/services/contentService.ts (integrate moderation check on content visibility)
• backend/src/middleware/rbac.ts (add moderator role checks)
• backend/migrations/ (new migration for moderation tables)
• backend/src/controllers/notificationController.ts (send moderation result notifications)

Acceptance Criteria

• User reports a course description as "Inappropriate content"; it appears in moderation queue with status "pending"
• Moderator reviews the report, clicks "Reject - Violates guidelines"; content is hidden and author gets notification
• Moderator approves a flagged post; it becomes visible and flag is cleared
• Auto-flagging catches content with blocked keywords before it becomes public
• Bulk approve/reject selects multiple queue items and applies action to all
• Non-moderator user gets 403 when accessing moderation endpoints
• Each moderation action is recorded in audit log with moderator ID, timestamp, reason

[ZuLu0890]

I would like to work on this issue within hours

[Kami-no-san]

hi i would like to work on this

[grantfox-oss]

🦊 GrantFox — @Kami-no-san has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #123)
2. Your PR will be reviewed by the Epondia maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@Kami-no-san's PR #139 was approved and merged by @jobbykings.

🏆 @Kami-no-san: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (818 total points). Track your full progress on GrantFox.

👏 Great work, @Kami-no-san! Keep contributing to Epondia.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@OmniZlatoon's PR #274 was approved and merged by @jobbykings.

🏆 @OmniZlatoon: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (153 total points). Track your full progress on GrantFox.

👏 Great work, @OmniZlatoon! Keep contributing to Epondia.