feat: accept usernames or UUIDs in follow management

admin/src/app/users/[id]/page.tsx

@@ -512,7 +512,7 @@ function FollowManager({ userId }: { userId: string }) {
 
       {/* Add */}
       <div className="flex items-center gap-2 mb-3">
-        <input type="text" placeholder="User ID to add" value={addHandle}
+        <input type="text" placeholder="Username or user ID" value={addHandle}
           onChange={(e) => setAddHandle(e.target.value)}
           onKeyDown={(e) => e.key === 'Enter' && handleAdd()}
           className="flex-1 px-2 py-1.5 border border-warm-300 rounded text-sm" />

go-backend/internal/handlers/admin_handler.go

@@ -689,6 +689,22 @@ func (h *AdminHandler) AdminUpdateProfile(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"message": "Profile updated"})
 }
 
+// resolveUserID accepts either a UUID or a handle and returns the user's UUID.
+func (h *AdminHandler) resolveUserID(ctx context.Context, input string) (string, error) {
+	// If it parses as a UUID, return as-is
+	if _, err := uuid.Parse(input); err == nil {
+		return input, nil
+	}
+	// Otherwise, treat as a handle and look it up
+	handle := strings.TrimPrefix(input, "@")
+	var id uuid.UUID
+	err := h.pool.QueryRow(ctx, `SELECT id FROM profiles WHERE handle = $1`, handle).Scan(&id)
+	if err != nil {
+		return "", fmt.Errorf("user not found: %s", input)
+	}
+	return id.String(), nil
+}
+
 // AdminManageFollow adds or removes follow relationships for official accounts.
 func (h *AdminHandler) AdminManageFollow(c *gin.Context) {
 	ctx := c.Request.Context()
@@ -696,7 +712,7 @@ func (h *AdminHandler) AdminManageFollow(c *gin.Context) {
 
 	var req struct {
 		Action   string `json:"action"`   // "add" or "remove"
-		UserID   string `json:"user_id"`  // the other user in the relationship
+		UserID   string `json:"user_id"`  // UUID or handle of the other user
 		Relation string `json:"relation"` // "follower" (user follows target) or "following" (target follows user)
 	}
 	if err := c.ShouldBindJSON(&req); err != nil {
@@ -713,16 +729,21 @@ func (h *AdminHandler) AdminManageFollow(c *gin.Context) {
 		return
 	}
 
+	// Resolve handle or UUID to a UUID
+	resolvedID, err := h.resolveUserID(ctx, req.UserID)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
 	// Determine follower_id and following_id
 	var followerID, followingID string
 	if req.Relation == "follower" {
-		// "user follows target" — user is follower, target is following
-		followerID = req.UserID
+		followerID = resolvedID
 		followingID = targetUserID
 	} else {
-		// "target follows user" — target is follower, user is following
 		followerID = targetUserID
-		followingID = req.UserID
+		followingID = resolvedID
 	}
 
 	if req.Action == "add" {