Adds server-side authentication hooks

[adenvt]

Implements server-side authentication hooks and custom error pages for improved extensibility and user experience.

• Introduces server-side plugins and context for handling authentication events.
• Provides hooks for customizing token requests, handling token refresh, and managing errors.
• Implements custom error pages to display user-friendly messages when authentication fails.
• Moves runtime logic to server routes and plugins for better organization.
• Updates dependencies and build configuration for server-side functionality.