feat: fix majority of bugs

[fanxiaotuGod]

Summary

This PR fixes a broad set of issues across the CREATE workflow and improves reliability, usability, and test coverage.

• Improved learning objective creation, editing, AI enrichment, regeneration, Bloom levels, subpoints, and linked-question handling.
• Enhanced the Coverage Map with better layout, filtering, search, node exploration, and source-evidence previews.
• Clarified course prompt responsibilities by separating editable instructions from locked CREATE guardrails and improving prompt validation.
• Improved quiz creation, sidebar synchronization, material previews, global search, onboarding, and generation progress logs.
• Fixed PDF/H5P export issues, including additional question-type support and Mark the Words normalization.
• Strengthened ownership validation, error handling, AI fallback behavior, and model compatibility.
• Added extensive frontend/backend regression tests and updated the CREATE Guide documentation.