feat(moderation): add manual content review system with three-tier AI moderation

Add admin comment moderation endpoints (single and batch) and introduce a three-tier moderation system (pass/review/block) for content flagged by AI. Content with unclear violations is now held for manual review instead of being auto-rejected. Deleted the legacy audit_service.go in favor of the unified hook-based moderation system.

internal/handler/comment_handler.go

@@ -2,7 +2,6 @@ package handler
 
 import (
 	"encoding/json"
-	"errors"
 	"strconv"
 
 	"github.com/gin-gonic/gin"
@@ -61,11 +60,6 @@ func (h *CommentHandler) Create(c *gin.Context) {
 
 	comment, err := h.commentService.Create(c.Request.Context(), req.PostID, userID, req.Content, req.ParentID, imagesJSON, req.Images)
 	if err != nil {
-		var moderationErr *service.CommentModerationRejectedError
-		if errors.As(err, &moderationErr) {
-			response.BadRequest(c, moderationErr.UserMessage())
-			return
-		}
 		response.InternalServerError(c, "failed to create comment")
 		return
 	}