- Move all default prompt content from PromptManager._ensure_* methods into aibox/prompts/ template files
- Add 8 new template files: 00_IDENTITY, 100_STATUS, 1_memory_search, 2_memory_save, 5_memo_management, 8_identity_management, 9_language_instruction, 11_emotion_management
- Refactor _ensure_* methods to copy from template directory via _ensure_from_template()
- _ensure_skill_files now auto-discovers N_*.md files instead of hardcoded list
- Update README.md with complete file manifest
- Single source of truth: aibox/prompts/ is the only prompt template source
