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

desktop/src-tauri/src/kernel_commands/mcp.rs

@@ -33,6 +33,7 @@ impl Default for McpManagerState {
 
 impl McpManagerState {
     /// Create with a pre-allocated kernel_adapters Arc for sharing with Kernel.
+    #[allow(dead_code)]
     pub fn with_shared_adapters(kernel_adapters: Arc<std::sync::RwLock<Vec<McpToolAdapter>>>) -> Self {
         Self {
             manager: Arc::new(Mutex::new(McpServiceManager::new())),