- migrate block content from plain strings to InlineNode[] structure
- add inline toolbar (bold, italic, code, color, link) on text selection
- add checklist block type with toggle support
- add image block type (URL-based, phase 2)
- add inline serialization helpers (inlineToDom, domToInline)
- add inline types and length utilities
- extend caret utils with range get/set support
- update block registry and all existing block types for new content model
- update demo blocks in ComponentsPage to use rich inline content
- update README to reflect new architecture
- import TagInput component and useState hook
- define ROLE_OPTIONS with color metadata for demo purposes
- add TagInputDemo wrapper component to manage local state
- add PreviewBlock showcasing default, colored badge, and error variants
- add `ZEN_DEVKIT` env variable to enable/disable devkit
- add `isDevkitEnabled()` utility and export it from public api
- register devkit nav section and items conditionally when devkit is enabled
- add devkit route handling in admin page client and server
- add DevkitPage, ComponentsPage, and IconsPage client components