feat(life): add reactions to life posts

Support 'like', 'helpful', 'fun', and 'thanks' reactions.
Add API endpoints and database schema for post reactions.
Update UI with reaction picker and summary counts.

frontend/src/i18n.ts

@@ -233,6 +233,16 @@ const messages = {
         commentsCount: '{count} comments',
         comment: 'Comment',
         hideComments: 'Hide comments',
+        react: 'Like',
+        reactions: 'Reactions',
+        reactionsCount: '{count} reactions',
+        reactionCountLabel: '{reaction}: {count}',
+        reactionLike: 'Like',
+        reactionHelpful: 'Helpful',
+        reactionFun: 'Fun',
+        reactionThanks: 'Thanks',
+        removeReaction: 'Remove reaction',
+        reactionFailed: 'Reaction failed',
         commentPlaceholder: 'Write a comment...',
         commentReplyPlaceholder: 'Write a reply...',
         postComment: 'Post comment',
@@ -566,6 +576,16 @@ const messages = {
         commentsCount: '{count} 条评论',
         comment: '评论',
         hideComments: '收起评论',
+        react: '点赞',
+        reactions: '互动',
+        reactionsCount: '{count} 次互动',
+        reactionCountLabel: '{reaction}：{count}',
+        reactionLike: '喜欢',
+        reactionHelpful: '有帮助',
+        reactionFun: '有趣',
+        reactionThanks: '感谢',
+        removeReaction: '取消互动',
+        reactionFailed: '互动失败',
         commentPlaceholder: '写下评论……',
         commentReplyPlaceholder: '写下回复……',
         postComment: '发表评论',