feat(posts): add post reference/internal linking functionality

Add support for referencing other posts within messages through a new post_ref segment type. Includes new PostReference model to track relationships, PostRefService for processing references, and new endpoints for post suggestions, related posts, and reference click tracking.

internal/dto/dto.go

@@ -250,8 +250,9 @@ const (
 	SegmentTypeAt    SegmentType = "at"
 	SegmentTypeReply SegmentType = "reply"
 	SegmentTypeFace  SegmentType = "face"
-	SegmentTypeLink  SegmentType = "link"
-	SegmentTypeVote  SegmentType = "vote"
+	SegmentTypeLink   SegmentType = "link"
+	SegmentTypeVote   SegmentType = "vote"
+	SegmentTypePostRef SegmentType = "post_ref"
 )
 
 // TextSegmentData 文本数据
@@ -325,6 +326,23 @@ type VoteOptionData struct {
 	Content string `json:"content"`
 }
 
+// PostRefSegmentData 帖子内链Segment数据
+type PostRefSegmentData struct {
+	PostID     string        `json:"post_id"`
+	Title      string        `json:"title,omitempty"`
+	Author     *UserResponse `json:"author,omitempty"`
+	Status     string        `json:"status,omitempty"`
+	Accessible bool          `json:"accessible"`
+	ClickCount int           `json:"click_count,omitzero"`
+}
+
+// PostRefBrief 帖子内链简要信息 (用于搜索联想)
+type PostRefBrief struct {
+	ID      string `json:"id"`
+	Title   string `json:"title"`
+	Channel string `json:"channel,omitempty"`
+}
+
 // VoteSegmentData 投票Segment数据
 type VoteSegmentData struct {
 	Options       []VoteOptionData `json:"options"`