Set up Go module and project structure

- Populated .gitignore with Go-specific patterns
- Created placeholder Go files with basic package structure:
  - bookstack.go: Client and Config setup
  - types.go: Data structures (Book, Page, Chapter, Shelf, SearchResult)
  - errors.go: Error handling types with sentinel errors
  - http.go: HTTP helper placeholder with ListOptions
  - books.go, pages.go, chapters.go, shelves.go, search.go: Service placeholders
- Verified build succeeds with go build ./...
- No external dependencies added (stdlib only)

All files compile successfully and follow flat package structure.

books.go

@@ -0,0 +1,43 @@
+package bookstack
+
+import "context"
+
+// BooksService handles operations on books.
+type BooksService struct {
+	client *Client
+}
+
+// List returns a list of books with optional filtering.
+// TODO: Implement API call to GET /api/books
+func (s *BooksService) List(ctx context.Context, opts *ListOptions) ([]Book, error) {
+	// Placeholder for future implementation
+	return nil, nil
+}
+
+// Get retrieves a single book by ID.
+// TODO: Implement API call to GET /api/books/{id}
+func (s *BooksService) Get(ctx context.Context, id int) (*Book, error) {
+	// Placeholder for future implementation
+	return nil, nil
+}
+
+// Create creates a new book.
+// TODO: Implement API call to POST /api/books
+func (s *BooksService) Create(ctx context.Context, book *Book) (*Book, error) {
+	// Placeholder for future implementation
+	return nil, nil
+}
+
+// Update updates an existing book.
+// TODO: Implement API call to PUT /api/books/{id}
+func (s *BooksService) Update(ctx context.Context, id int, book *Book) (*Book, error) {
+	// Placeholder for future implementation
+	return nil, nil
+}
+
+// Delete deletes a book by ID.
+// TODO: Implement API call to DELETE /api/books/{id}
+func (s *BooksService) Delete(ctx context.Context, id int) error {
+	// Placeholder for future implementation
+	return nil
+}