Add initial project structure with core functionality for book and stationery uploads

- Created main application entry point in `main.go`.
- Added configuration management in `config/config.go` and tests in `config/config_test.go`.
- Implemented handlers for book and stationery uploads in `handlers/book.go` and `handlers/stationery.go`, including validation logic.
- Established database connection and services in `services/database.go` and `services/book_service.go`.
- Defined models for books and stationery in `models/book.go` and `models/stationery.go`.
- Set up Firebase integration for image uploads in `services/firebase.go`.
- Created migration scripts for database schema in `migrations/001_create_tables.sql` and subsequent updates.
- Added CORS and error handling middleware.
- Included comprehensive tests for handlers, services, and utilities.
- Documented API endpoints and usage in `README.md` and migration instructions in `migrations/README.md`.
- Introduced `.gitignore` to exclude unnecessary files and directories.
- Added Go module support with `go.mod` and `go.sum` files.
- Implemented utility functions for slug generation and validation in `utils/slug.go` and `utils/validation.go`.

middleware/cors.go

@@ -0,0 +1,20 @@
+package middleware
+
+import (
+	"jd-book-uploader/config"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/gofiber/fiber/v2/middleware/cors"
+)
+
+// SetupCORS configures CORS middleware based on application config
+func SetupCORS(cfg *config.Config) fiber.Handler {
+	return cors.New(cors.Config{
+		AllowOrigins:     cfg.FrontendURL,
+		AllowMethods:     "GET,POST,PUT,DELETE,OPTIONS",
+		AllowHeaders:     "Origin,Content-Type,Accept,Authorization",
+		AllowCredentials: true,
+		ExposeHeaders:    "Content-Length",
+		MaxAge:           3600, // 1 hour
+	})
+}