chore: Cargo warnings 清零 — 39→0 (仅剩 sqlx-postgres 外部依赖警告)

- runtime: 移除未使用的 SessionId/Datelike import，修复 unused variable
- intelligence: 模块级 #![allow(dead_code)] 抑制 Hermes 预留代码警告
- mcp.rs/persist.rs/nl_schedule.rs: 标注 #[allow(dead_code)] 保留接口

crates/zclaw-runtime/src/nl_schedule.rs

@@ -7,7 +7,7 @@
 //!
 //! Lives in `zclaw-runtime` because it's a pure text→cron utility with no kernel dependency.
 
-use chrono::{Datelike, Timelike};
+use chrono::Timelike;
 use serde::{Deserialize, Serialize};
 use zclaw_types::AgentId;
 
@@ -60,6 +60,7 @@ pub enum ScheduleParseResult {
 // ---------------------------------------------------------------------------
 
 /// A single pattern for matching Chinese time expressions.
+#[allow(dead_code)]
 struct SchedulePattern {
     /// Regex pattern string
     regex: &'static str,