feat(life): require at least one tag for life posts

Update design spec to mandate tag selection
Add frontend and backend validation for tag requirement
Add localization strings for tag required errors

system-wordings.ts

@@ -436,6 +436,7 @@ export const systemWordingMessages = {
         saveFailed: 'Save failed',
         deleteFailed: 'Delete failed',
         bodyRequired: 'Please enter a post.',
+        tagRequired: 'Please select at least one tag.',
         byUnknown: 'Community member',
         edited: 'Edited',
         deleteConfirm: 'Delete this post?',
@@ -648,6 +649,7 @@ export const systemWordingMessages = {
       taskDoesNotExist: 'Task does not exist',
       postRequired: 'Please enter a post',
       postTooLong: 'Post is too long',
+      lifeTagRequired: 'Please select at least one tag',
       commentRequired: 'Please enter a comment',
       commentTooLong: 'Comment is too long',
       reactionInvalid: 'Reaction is invalid',
@@ -1144,6 +1146,7 @@ export const systemWordingMessages = {
         saveFailed: '保存失败',
         deleteFailed: '删除失败',
         bodyRequired: '请输入动态内容。',
+        tagRequired: '请至少选择 1 个标签。',
         byUnknown: '社区成员',
         edited: '已编辑',
         deleteConfirm: '确认删除这条动态？',
@@ -1356,6 +1359,7 @@ export const systemWordingMessages = {
         taskDoesNotExist: '任务不存在',
         postRequired: '请输入动态内容',
         postTooLong: '动态内容过长',
+        lifeTagRequired: '请至少选择 1 个标签',
         commentRequired: '请输入评论内容',
         commentTooLong: '评论内容过长',
         reactionInvalid: '互动类型不合法',