feat: add post mention

internal/model/social.go

@@ -46,6 +46,10 @@ type Post struct {
 	// false for anonymous viewers.
 	LikesCount     int  `json:"likes_count"`
 	ViewerHasLiked bool `json:"viewer_has_liked"`
+
+	// MentionsCount is how many users are tagged on this post (drives the
+	// post-card mentions icon). Hydrated by the mention layer.
+	MentionsCount int `json:"mentions_count"`
 }
 
 // PostImage represents one attached image on a post.

internal/model/user.go

@@ -15,6 +15,9 @@ import (
 // UserSummary is the lightweight projection used in follower / following
 // lists — just enough to render a row and link to the profile.
 type UserSummary struct {
+	// ID is populated only where the caller needs it (e.g. mention add/remove);
+	// omitted from follower/like lists that link by handle.
+	ID        string  `json:"id,omitempty"`
 	Handle    string  `json:"handle"`
 	Name      string  `json:"name"`
 	AvatarURL *string `json:"avatar_url"`