fix(audit): Batch 4-6 中间件注释 + 依赖迁移 + 安全加固

Batch 4:
- kernel/mod.rs: 添加中间件注册顺序≠执行顺序注释
- EvolutionMiddleware 注册处标注 priority=78

Batch 5:
- desktop/src-tauri/Cargo.toml: serde_yaml 0.9 (deprecated) → serde_yaml_bw 2.x

Batch 6:
- saas/main.rs: CORS 开发模式改为显式 localhost origins (修复 Any+credentials 违规)
- docker-compose.yml: 移除默认弱密码 your_secure_password，改为必填校验
- director.rs: 用户输入添加 <user_input>/<user_request> 边界标记防注入

全量测试通过: 719 passed, 0 failed

desktop/src-tauri/Cargo.toml

@@ -47,7 +47,7 @@ async-trait = { workspace = true }
 # Serialization
 serde = { workspace = true }
 serde_json = { workspace = true }
-serde_yaml = "0.9"
+serde_yaml = { package = "serde_yaml_bw", version = "2" }
 toml = "0.8"
 
 # HTTP client