docs: define learning quality standards

[v-liuxingan]

Summary

• add a complete teaching SOP from preparation and diagnosis through independent practice, transfer, reteaching, and evidence-based closure
• add a learning project initialization SOP covering learner diagnosis, capability mapping, milestones, CLI registration, content materialization, review setup, and acceptance
• define quality and format gates for roadmaps, resources, notes, exercises, projects, flashcards, reviews, progress, and session records
• enforce the learning-process-manager top-level directory contract and reject parallel state/review structures
• route learning-guide to the required references by task type and reject unfinished template placeholders

Closes #11

Verification

• skill-creator quick_validate.py
• npm run verify
• 7 unit tests and 4 end-to-end tests
• npm audit: 0 vulnerabilities
• forward-test: full OceanBase tenant lesson
• forward-test: OceanBase project initialization structure after reading all required references

Notes

• The first structure test intentionally exposed that a directory contract hidden only in a reference was too weak; the invariant now also lives in SKILL.md.
• Existing untracked release artifacts are not included.