feat: community post/comment/reply reactions (#809)

[clbotdev]

Summary

Evolve the community post/comment/reply like system to support multiple emoji reactions. Closes #809.

Changes

Backend:

• New CommunityReaction type in common-models with emoji, count, hasReacted, reactors fields
• Updated CommunityPost, CommunityComment, CommunityCommentReply interfaces to include reactions: CommunityReaction[]
• Schema: replaced likes: [String] with reactions: { type: Map, of: [String], default: {} } on all three schemas. Kept likes: [String] for backward compatibility with existing data.
• New GraphQL mutations: togglePostReaction, toggleCommentReaction, toggleCommentReplyReaction accepting emoji: String!
• New field resolvers: getReactionsForEntity() populates reactor details (name, avatar)
• Backward compatibility: existing likes: string[] data is automatically read as ❤️ reactions via getReactionsMap() fallback
• Migration script to convert existing likes to reactions format

Frontend:

• New emoji-picker.tsx — emoji picker popover with common reactions (👍 ❤️ 😄 🎉 😢 😮)
• New reactions-bar.tsx — displays reaction emojis with counts, highlights user reactions, "+" button for picker, hover tooltip with reactor names
• Updated post-card.tsx — replaced ThumbsUp button with reactions bar
• Updated comment.tsx — replaced ThumbsUp on comments/replies with compact reactions bar
• Updated comment-section.tsx — updated GraphQL queries/mutations for reactions

Technical notes:

• All 641 tests pass, lint clean, prettier clean
• ES5 target compatibility: Map iteration rewritten to use .forEach() instead of for...of