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.Application/Features/Books/Commands/PublishBookVersionCommand.cs

@@ -0,0 +1,12 @@
+using NexusReader.Application.Abstractions.Messaging;
+
+namespace NexusReader.Application.Features.Books.Commands;
+
+/// <summary>
+/// Command to publish a new frozen version of a Book, and create a new Working Draft.
+/// </summary>
+/// <param name="BookId">The unique identifier of the Book to publish.</param>
+/// <param name="CustomVersionString">The custom version string to apply (e.g. "v1.0").</param>
+/// <param name="UserId">The ID of the user requesting the action.</param>
+/// <param name="TenantId">The tenant ID for multi-tenant isolation.</param>
+public record PublishBookVersionCommand(Guid BookId, string CustomVersionString, string UserId, string TenantId) : ICommand;