feat(api): add message segments support for posts and comments

Add rich message segment support enabling structured content (text, images, votes, mentions) in posts and comments. Includes segments field in models, DTOs, handlers, and services. Also adds @mention notification processing and migrates vote data to embedded segments.

internal/handler/post_handler.go

@@ -1,4 +1,4 @@
-package handler
+package handler
 
 import (
 	"errors"
@@ -52,20 +52,21 @@ func (h *PostHandler) Create(c *gin.Context) {
 		return
 	}
 
-	type CreateRequest struct {
-		Title     string   `json:"title" binding:"required"`
-		Content   string   `json:"content" binding:"required"`
-		Images    []string `json:"images"`
-		ChannelID *string  `json:"channel_id,omitempty"`
-	}
-
-	var req CreateRequest
+	var req dto.CreatePostWithSegmentsRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
 		response.BadRequest(c, err.Error())
 		return
 	}
 
-	post, err := h.postService.Create(c.Request.Context(), userID, req.Title, req.Content, req.Images, req.ChannelID)
+	content := req.Content
+	segments := req.Segments
+
+	if len(segments) == 0 && content == "" {
+		response.BadRequest(c, "content or segments is required")
+		return
+	}
+
+	post, err := h.postService.Create(c.Request.Context(), userID, req.Title, content, segments, req.Images, req.ChannelID)
 	if err != nil {
 		var moderationErr *service.PostModerationRejectedError
 		if errors.As(err, &moderationErr) {
@@ -123,6 +124,7 @@ func (h *PostHandler) GetByID(c *gin.Context) {
 		ChannelID:       post.ChannelID,
 		Title:           post.Title,
 		Content:         post.Content,
+		Segments:        dto.SegmentsOrDefault(post.Segments, post.Content),
 		Images:          dto.ConvertPostImagesToResponse(post.Images),
 		Status:          string(post.Status),
 		LikesCount:      post.LikesCount,
@@ -365,9 +367,10 @@ func (h *PostHandler) Update(c *gin.Context) {
 	}
 
 	type UpdateRequest struct {
-		Title   string    `json:"title"`
-		Content string    `json:"content"`
-		Images  *[]string `json:"images"`
+		Title    string                `json:"title"`
+		Content  string                `json:"content"`
+		Segments model.MessageSegments `json:"segments"`
+		Images   *[]string             `json:"images"`
 	}
 
 	var req UpdateRequest
@@ -382,6 +385,12 @@ func (h *PostHandler) Update(c *gin.Context) {
 	if req.Content != "" {
 		post.Content = req.Content
 	}
+	if len(req.Segments) > 0 {
+		post.Segments = req.Segments
+		if req.Content == "" {
+			post.Content = dto.ExtractTextContent(req.Segments)
+		}
+	}
 
 	err = h.postService.UpdateWithImages(c.Request.Context(), post, req.Images)
 	if err != nil {