feat: 六爻算法修复 + prompt架构重构 + i18n输出规则

算法修复 (P0/P1):
- P0-1: 空亡判断改为仅从日柱计算（年月空亡标注但不断事）
- P0-2: 暗动判断重写为静爻+旺相+日冲三条件
- P1-1: 月破独立标注
- P1-2: 动不为空、旺不为空
- P1-3: 三合局判断
- P1-4: 反吟伏吟判断
- P1-5: 日辰十二长生
- P1-6: 回头生克判断

Prompt架构重构:
- 删除system_prompt中_build_env_section，不再泄露用户上下文到prompt
- 删除if is_chinese分支，_LANGUAGE_LABELS已覆盖全部语言映射
- 安全规则改为六爻专属约束，拒绝无关问题
- sign_level枚举值在所有语言版本中统一为简体中文（schema严格约束）
- _WORKER_ROLE_PLAYING始终为中文，不因ai_language切换
- _WORKER_OUTPUT_RULES按ai_language分zh-CN/zh-Hant/en三版本
- worker_rules.py独立文件管理多语言输出规则
- runner ai_language从user_context.settings.preferences提取传入prompt

清理死代码:
- 删除UserPreferences/RuntimePromptContext及辅助函数
- 删除runner中runtime_client_time参数链路
- 删除SystemAgentRuntimeConfig.extra_context
- 删除sections.py中env section marker
- 删除agent_prompt.py中AgentPromptRegistry死代码

安全规则:
- AGENTS.md添加Git Safety规则（禁止未经批准的破坏性git操作）
- opencode.json添加高危git命令审批配置

测试:
- 新增22个六爻算法单元测试（空亡/暗动/月破/三合局等）
- 重写7个prompt测试适配新签名
- 全部85个单元测试通过

AGENTS.md

@@ -30,6 +30,14 @@ Do not place backend/frontend implementation details here.
 - Keep AGENTS layered and lean: shared rules at root, domain rules in sub-AGENTS.
 - **No Error Swallowing**: All exceptions must propagate or be converted to typed errors. Never catch an exception, log it, and silently continue. This destroys debuggability.
 
+## Git Safety (CRITICAL)
+
+- **NEVER execute `git checkout -- <file>` or any git command that modifies files without explicit user approval.**
+- **NEVER reset, revert, or discard uncommitted changes without user consent.**
+- If you need to discard changes, ask the user first and explain exactly what will be lost.
+- Before any destructive git operation, list the affected files and get confirmation.
+- This rule is non-negotiable. Violation will cause irreversible loss of user work.
+
 ## Protocol Source of Truth
 
 `docs/protocols/` is the single source of truth for protocol and data format.