feat(lesson-preparation): add anchor canvas design, new blocks, and textbook content node
- Add anchor injector for canvas-based anchor positioning
- Add new block components: blackboard, homework, import, key-point, new-teaching, objective, summary
- Add textbook content node for React Flow canvas
- Update actions (kp, publish, main), data-access (templates, versions, main)
- Update editor, node-editor, block-renderer, and picker components
- Update schema, types, hooks, and lib utilities (document-migration, node-summary, rf-mappers)
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