feat(workspace): stack hashtag back button above heading and add dedicated hashtag markdown note (#tag.md)

internal/api/server.go

@@ -106,6 +106,7 @@ func (s *Server) Router() http.Handler {
 		// Workspace Tags & Pages
 		r.Get("/api/v1/workspace/tags", s.handleGetWorkspaceTags)
 		r.Get("/api/v1/workspace/tags/{tag}", s.handleGetTagDetails)
+		r.Put("/api/v1/workspace/tags/{tag}/note", s.handleUpdateTagPageNote)
 
 		r.Get("/api/v1/documents", s.handleGetDocuments)
 		r.Post("/api/v1/documents", s.handleCreateDocument)
@@ -903,6 +904,28 @@ func (s *Server) handleGetTagDetails(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, details)
 }
 
+func (s *Server) handleUpdateTagPageNote(w http.ResponseWriter, r *http.Request) {
+	userID := auth.GetUserID(r.Context())
+	tag := chi.URLParam(r, "tag")
+	var req struct {
+		Content string `json:"content"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "Ungültiges JSON")
+		return
+	}
+	updatedAt, err := s.store.UpdateTagPageNote(userID, tag, req.Content)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]string{
+		"tag":       tag,
+		"content":   req.Content,
+		"updatedAt": updatedAt,
+	})
+}
+
 // --- DOCUMENT SHARING & COLLABORATION ---
 
 func (s *Server) handleGetDocShares(w http.ResponseWriter, r *http.Request) {