fix(handlers): normalize filename to prevent double .md extension

Strip .md suffix from filename when creating files to prevent
filename.md.md from being created. This aligns with the behavior
in FileHandler which also normalizes filenames from URLs.

Fixes issue where files created with .md extension could not be
deleted due to filename mismatch.

backend/handlers/handlers.go

@@ -104,7 +104,10 @@ func (h *Handler) createFile(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if err := h.storage.Save(req.Name, req.Content); err != nil {
+	// Normalize filename by stripping .md extension if present
+	name := strings.TrimSuffix(req.Name, ".md")
+
+	if err := h.storage.Save(name, req.Content); err != nil {
 		h.log.WithError(err).Error("Failed to create file")
 		h.sendError(w, http.StatusInternalServerError, "failed to create file")
 		return
@@ -112,7 +115,7 @@ func (h *Handler) createFile(w http.ResponseWriter, r *http.Request) {
 
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusCreated)
-	json.NewEncoder(w).Encode(FileResponse{Name: req.Name, Content: req.Content})
+	json.NewEncoder(w).Encode(FileResponse{Name: name, Content: req.Content})
 }
 
 func (h *Handler) getFile(w http.ResponseWriter, r *http.Request, name string) {