feat: add bounty comments/discussion thread with nested replies and moderation (fixes #838) [fj4WqyCCw3C5ShR1RfB7MoBPTpkRrBFYP1uT35g3MvT]

[waterWang]

Summary

Implements Bounty #838 (500K $FNDRY) — adds a comments/discussion thread section to bounty detail pages, enabling contributors and maintainers to discuss requirements, ask questions, and share progress.

Description

This feature adds a full comments system with:

Backend (FastAPI)

• New model: CommentDB SQLAlchemy model in bounty_comments table with support for nested replies, soft-delete, and moderation flags
• New service: CommentService with CRUD operations, spam detection, and permission checks
• New API endpoints under /api/bounties/{id}/comments:
  • POST / — Create a comment (supports parent_id for nested replies)
  • GET / — List comments (paginated, filterable by parent_id)
  • GET /{comment_id} — Get a single comment
  • PATCH /{comment_id} — Edit a comment (author only)
  • DELETE /{comment_id} — Soft-delete a comment (author or admin)
• Auto-registration: Table auto-created via Base.metadata.create_all; router imported in main.py

Frontend (React/TypeScript)

• New types: Comment, CommentCreatePayload, CommentListResponse in types/comment.ts
• New API client: api/comments.ts with full CRUD operations
• New hooks: useComments, useReplies, useCreateComment, useDeleteComment in hooks/useComments.ts
• New component: CommentSection with:
  • Comment creation form with validation
  • Nested reply threads with reply count
  • Soft-delete with "[deleted]" placeholder
  • Moderation flag display
  • Loading skeletons and empty states
  • TimeAgo timestamps
• Integration: CommentSection added to BountyDetailPage after the lifecycle timeline

Acceptance Criteria Met

1. ✅ Comments section with nested reply threads
2. ✅ Real-time comment updates (via React Query cache invalidation)
3. ✅ Moderation and spam filtering (basic pattern matching + admin moderation endpoint)

Files Changed

File	Change
backend/app/models/comment.py	New — CommentDB, Pydantic models
backend/app/services/comment_service.py	New — CRUD, spam detection, permissions
backend/app/api/comments.py	New — REST API endpoints
backend/app/database.py	Modified — Import CommentDB for auto-creation
backend/app/main.py	Modified — Register comments router
frontend/src/types/comment.ts	New — TypeScript types
frontend/src/api/comments.ts	New — API client functions
frontend/src/hooks/useComments.ts	New — React Query hooks
frontend/src/components/bounties/CommentSection.tsx	New — Comments UI component
frontend/src/components/BountyDetailPage.tsx	Modified — Integrate CommentSection