Add project import and learning status commands

[v-liuxingan]

Summary

• Add learn project import to register an existing learning directory without replacing existing project files.
• Add Agent-friendly learn status and learn next commands with project, review, recent-session, and next-action summaries.
• Remove misleading review --strategy and replace the nonexistent flashcard generate suggestion with real commands.
• Update README, AGENTS.md, and both learning skills to match the new CLI surface.

Closes #7

Validation

• npm run typecheck
• npm run test:run
• npm run build
• npm run test:e2e
• npm run lint
• PYTHONUTF8=1 python C:\Users\admin\.codex\skills\.system\skill-creator\scripts\quick_validate.py E:\develop\projects\AiProjects\learning-process-manager\skills\learning-cli
• PYTHONUTF8=1 python C:\Users\admin\.codex\skills\.system\skill-creator\scripts\quick_validate.py E:\develop\projects\AiProjects\learning-process-manager\skills\learning-guide