Add theme editing to the existing PageEditorHook, enabling on-site
theme customisation alongside page editing. The editor panel now has
three tabs (Page, Theme, Settings) and can be collapsed while
keeping editing state intact.
- Add theme editing state and event handlers to PageEditorHook
- Add 3-tab UI with tab switching logic
- Add transparent overlay for click-outside dismiss
- Add mobile drag-to-resize with height persistence
- Fix animation replay on drag release (has-dragged class)
- Preserve panel height across LiveView re-renders
- Default to Page tab on editable pages, Theme otherwise
- Show unsaved changes indicator on FAB when panel collapsed
- Fix handle_event grouping warning in admin theme
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
