docs: improve learning guide orchestration

[v-liuxingan]

Summary

• turn learning-guide into a stateful session orchestrator with explicit mode and conflict decisions
• require one primary learner action per turn and observable recall/explanation/application/transfer evidence
• add safe project import, review scoring, session lifecycle, flashcard quality, and failure recovery rules
• move detailed pedagogy into a progressively loaded teaching playbook
• refresh the skill UI metadata

Closes #9

Verification

• skill-creator quick_validate.py
• npm run lint
• npm run typecheck
• npm run test:run (7 tests)
• npm run build
• npm run test:e2e (4 tests)
• npm audit executed; existing brace-expansion and postcss advisories remain
• forward-tested against a 15-minute OceanBase continuation prompt

Notes

• No CLI implementation or data model changes are included.
• Existing untracked release artifacts were not committed.