feat(creator): Refactor Creator flow, implement book creation pipeline & versioning, and setup Docker staging

- Relocate dashboard routing to /creator and editor workspace to /creator/edit/{BookId}
- Implement CreateBookCommand and handler with transactional default chapter seeding
- Implement PublishBookVersionCommand and GetCreatorDashboardDataQuery
- Build CreatorDashboard modal and UI components with customized dark input styles
- Add run-stage.sh script to automate staging environment setup, database migrations, and health checks
- Update developer workflow rules in GEMINI.md

src/NexusReader.Domain/Entities/BookRevision.cs

@@ -0,0 +1,31 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace NexusReader.Domain.Entities;
+
+/// <summary>
+/// Encapsulates a snapshot or draft version of a Book's chapters.
+/// </summary>
+public class BookRevision
+{
+    [Key]
+    public Guid Id { get; set; } = Guid.NewGuid();
+
+    [Required]
+    public Guid BookId { get; set; }
+
+    [ForeignKey(nameof(BookId))]
+    public virtual Book Book { get; set; } = null!;
+
+    [Required]
+    [MaxLength(100)]
+    public string VersionString { get; set; } = "Working Draft";
+
+    public bool IsPublished { get; set; } = false;
+
+    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+
+    public DateTime? PublishedAt { get; set; }
+
+    public virtual ICollection<Chapter> Chapters { get; set; } = new List<Chapter>();
+}