fix: resolve JSON.parse error in frontend API calls

- Add error handling for JSON encoding in all backend handlers
- Add CORS support to backend server
- Add proxy configuration for frontend development server
- Improve error handling in frontend API calls
- Build frontend to create static files for backend serving
- Add comprehensive error messages and user feedback

Fixes issue where frontend received malformed JSON responses from backend API.

backend/internal/handlers/handlers.go

@@ -31,9 +31,13 @@ func (h *Handlers) ListFiles() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		if err := json.NewEncoder(w).Encode(map[string]interface{}{
 			"files": files,
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -62,9 +66,13 @@ func (h *Handlers) CreateFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{
+		if err := json.NewEncoder(w).Encode(map[string]string{
 			"message": "file created successfully",
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -86,10 +94,14 @@ func (h *Handlers) GetFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]interface{}{
+		if err := json.NewEncoder(w).Encode(map[string]interface{}{
 			"filename": filename,
 			"content":  string(content),
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -120,9 +132,13 @@ func (h *Handlers) UpdateFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{
+		if err := json.NewEncoder(w).Encode(map[string]string{
 			"message": "file updated successfully",
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
@@ -143,16 +159,23 @@ func (h *Handlers) DeleteFile() http.HandlerFunc {
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{
+		if err := json.NewEncoder(w).Encode(map[string]string{
 			"message": "file deleted successfully",
-		})
+		}); err != nil {
+			h.logger.Errorf("Failed to encode response: %v", err)
+			h.writeError(w, http.StatusInternalServerError, "failed to encode response")
+			return
+		}
 	}
 }
 
 func (h *Handlers) writeError(w http.ResponseWriter, status int, message string) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)
-	json.NewEncoder(w).Encode(map[string]string{
+	if err := json.NewEncoder(w).Encode(map[string]string{
 		"error": message,
-	})
+	}); err != nil {
+		h.logger.Errorf("Failed to encode error response: %v", err)
+		w.Write([]byte(`{"error": "failed to encode error response"}`))
+	}
 }