Add post image storage (#10)

Adds migration 010, ordered attachment metadata, and transaction-safe image persistence for posts and replies.

Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/store/sqlc/models.go

@@ -22,6 +22,18 @@ type Post struct {
 	UpdatedAt string
 }
 
+type PostImage struct {
+	ID          string
+	PostID      string
+	ObjectKey   string
+	PublicUrl   string
+	Description string
+	Position    int16
+	Width       int32
+	Height      int32
+	CreatedAt   string
+}
+
 type PostVote struct {
 	UserID string
 	PostID string