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`.

services/database_test.go

@@ -0,0 +1,57 @@
+package services
+
+import (
+	"testing"
+	"time"
+
+	"jd-book-uploader/config"
+)
+
+func TestNewDBPool(t *testing.T) {
+	// This test requires a running PostgreSQL instance
+	// Skip if not available
+	t.Skip("Skipping database connection test - requires running PostgreSQL")
+
+	cfg := &config.Config{
+		DBHost:     "localhost",
+		DBPort:     "5432",
+		DBUser:     "test_user",
+		DBPassword: "test_password",
+		DBName:     "test_db",
+	}
+
+	pool, err := NewDBPool(cfg)
+	if err != nil {
+		t.Fatalf("NewDBPool() error = %v", err)
+	}
+	defer pool.Close()
+
+	if pool == nil {
+		t.Error("NewDBPool() returned nil pool")
+	}
+}
+
+func TestRetryConnection(t *testing.T) {
+	// This test requires a running PostgreSQL instance
+	// Skip if not available
+	t.Skip("Skipping database retry test - requires running PostgreSQL")
+
+	cfg := &config.Config{
+		DBHost:     "localhost",
+		DBPort:     "5432",
+		DBUser:     "test_user",
+		DBPassword: "test_password",
+		DBName:     "test_db",
+	}
+
+	pool, err := RetryConnection(cfg, 3, time.Second)
+	if err != nil {
+		t.Logf("RetryConnection() error = %v (expected if DB not available)", err)
+		return
+	}
+	defer pool.Close()
+
+	if pool == nil {
+		t.Error("RetryConnection() returned nil pool")
+	}
+}