feat(phase3): forum channels + tags + card UI

internal/channel/threads.go

@@ -11,8 +11,9 @@ import (
 )
 
 type createThreadRequest struct {
-	Name      string  `json:"name"`
-	MessageID *string `json:"message_id,omitempty"`
+	Name      string   `json:"name"`
+	MessageID *string  `json:"message_id,omitempty"`
+	TagIDs    []string `json:"tag_ids,omitempty"`
 }
 
 type threadResponse struct {
@@ -95,6 +96,16 @@ func (h *Handler) CreateThread(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Attach optional tags for forum posts.
+	if len(req.TagIDs) > 0 {
+		// ponytail: ignore tag errors; best-effort assignment
+		for _, tagID := range req.TagIDs {
+			_, _ = h.db.ExecContext(r.Context(), `
+				INSERT INTO channel_tags (channel_id, tag_id) VALUES ($1, $2) ON CONFLICT DO NOTHING
+			`, thread.ID, tagID)
+		}
+	}
+
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusCreated)
 	json.NewEncoder(w).Encode(thread)