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.

types.go

@@ -0,0 +1,76 @@
+package bookstack
+
+import "time"
+
+// Book represents a Bookstack book.
+type Book struct {
+	ID          int       `json:"id"`
+	Name        string    `json:"name"`
+	Slug        string    `json:"slug"`
+	Description string    `json:"description"`
+	CreatedAt   time.Time `json:"created_at"`
+	UpdatedAt   time.Time `json:"updated_at"`
+	CreatedBy   int       `json:"created_by"`
+	UpdatedBy   int       `json:"updated_by"`
+	OwnedBy     int       `json:"owned_by"`
+}
+
+// Page represents a Bookstack page.
+type Page struct {
+	ID        int       `json:"id"`
+	BookID    int       `json:"book_id"`
+	ChapterID int       `json:"chapter_id"`
+	Name      string    `json:"name"`
+	Slug      string    `json:"slug"`
+	HTML      string    `json:"html"`
+	Markdown  string    `json:"markdown"`
+	Priority  int       `json:"priority"`
+	CreatedAt time.Time `json:"created_at"`
+	UpdatedAt time.Time `json:"updated_at"`
+	CreatedBy int       `json:"created_by"`
+	UpdatedBy int       `json:"updated_by"`
+	Draft     bool      `json:"draft"`
+	Revision  int       `json:"revision_count"`
+	Template  bool      `json:"template"`
+	OwnedBy   int       `json:"owned_by"`
+}
+
+// Chapter represents a Bookstack chapter.
+type Chapter struct {
+	ID          int       `json:"id"`
+	BookID      int       `json:"book_id"`
+	Name        string    `json:"name"`
+	Slug        string    `json:"slug"`
+	Description string    `json:"description"`
+	Priority    int       `json:"priority"`
+	CreatedAt   time.Time `json:"created_at"`
+	UpdatedAt   time.Time `json:"updated_at"`
+	CreatedBy   int       `json:"created_by"`
+	UpdatedBy   int       `json:"updated_by"`
+	OwnedBy     int       `json:"owned_by"`
+}
+
+// Shelf represents a Bookstack shelf.
+type Shelf struct {
+	ID          int       `json:"id"`
+	Name        string    `json:"name"`
+	Slug        string    `json:"slug"`
+	Description string    `json:"description"`
+	CreatedAt   time.Time `json:"created_at"`
+	UpdatedAt   time.Time `json:"updated_at"`
+	CreatedBy   int       `json:"created_by"`
+	UpdatedBy   int       `json:"updated_by"`
+	OwnedBy     int       `json:"owned_by"`
+}
+
+// SearchResult represents a search result from Bookstack.
+type SearchResult struct {
+	Type      string  `json:"type"` // "page", "chapter", "book", or "shelf"
+	ID        int     `json:"id"`
+	Name      string  `json:"name"`
+	Slug      string  `json:"slug"`
+	BookID    int     `json:"book_id"`    // For pages and chapters
+	ChapterID int     `json:"chapter_id"` // For pages
+	Preview   string  `json:"preview"`
+	Score     float64 `json:"score"`
+}