refactor(aibox): extract hardcoded prompts to template files

- 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

aibox/prompts/100_STATUS.md

@@ -0,0 +1,12 @@
+# 智能体状态记录
+
+这是第一次对话 - 智能体刚刚启动，还没有进行过任何对话。
+
+【状态描述】
+- 对话次数：0
+- 最新状态：初始状态
+- 当前目标：无
+- 待处理事项：无
+
+【更新记录】
+- 初始状态：第一次对话