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`.

migrations/003_add_unique_slug_constraints.sql

@@ -0,0 +1,43 @@
+-- Add UNIQUE constraint to slug columns in both books and stationery tables
+-- This prevents duplicate slugs and enables slug-based image filename uniqueness
+
+-- First, handle any existing duplicate slugs by appending a suffix
+-- For books
+UPDATE books b1
+SET slug = slug || '-' || book_code::text
+WHERE EXISTS (
+    SELECT 1 FROM books b2
+    WHERE b2.slug = b1.slug
+    AND b2.book_code < b1.book_code
+);
+
+-- For stationery
+UPDATE stationery s1
+SET slug = slug || '-' || stationery_code::text
+WHERE EXISTS (
+    SELECT 1 FROM stationery s2
+    WHERE s2.slug = s1.slug
+    AND s2.stationery_code < s1.stationery_code
+);
+
+-- Add unique constraint to books.slug (if not exists)
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint 
+        WHERE conname = 'books_slug_unique'
+    ) THEN
+        ALTER TABLE books ADD CONSTRAINT books_slug_unique UNIQUE (slug);
+    END IF;
+END $$;
+
+-- Add unique constraint to stationery.slug (if not exists)
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint 
+        WHERE conname = 'stationery_slug_unique'
+    ) THEN
+        ALTER TABLE stationery ADD CONSTRAINT stationery_slug_unique UNIQUE (slug);
+    END IF;
+END $$;