fix: 发布前审计 Batch 2 — Debug遮蔽 + unwrap + 静默吞错 + MCP锁 + 索引 + Config验证

安全:
- LlmConfig 自定义 Debug impl，api_key 显示为 "***REDACTED***"
- tsconfig.json 移除 ErrorBoundary.tsx 排除项（安全关键组件）
- billing/handlers.rs Response builder unwrap → map_err 错误传播
- classroom_commands/mod.rs db_path.parent().unwrap() → ok_or_else

静默吞错:
- approvals.rs 3处 warn→error（审批状态丢失是严重事件）
- events.rs publish() 添加 Event dropped debug 日志
- mcp_transport.rs eprintln→tracing::warn (僵尸进程风险)
- zclaw-growth sqlite.rs 4处迁移：区分 duplicate column name 与真实错误

MCP Transport:
- 合并 stdin+stdout 为单一 Mutex<TransportHandles>
- send_request write-then-read 原子化，防止并发响应错配

数据库:
- 新迁移 20260418000001: idx_rle_created_at + idx_billing_sub_plan + idx_ki_created_by

配置验证:
- SaaSConfig::load() 添加 jwt_expiration_hours>=1, max_connections>0, min<=max

crates/zclaw-kernel/src/kernel/approvals.rs

@@ -86,12 +86,12 @@ impl Kernel {
                     completed_at: None,
                 };
                 let _ = memory.save_hand_run(&run).await.map_err(|e| {
-                    tracing::warn!("[Approval] Failed to save hand run: {}", e);
+                    tracing::error!("[Approval] Failed to save hand run: {}", e);
                 });
                 run.status = HandRunStatus::Running;
                 run.started_at = Some(chrono::Utc::now().to_rfc3339());
                 let _ = memory.update_hand_run(&run).await.map_err(|e| {
-                    tracing::warn!("[Approval] Failed to update hand run (running): {}", e);
+                    tracing::error!("[Approval] Failed to update hand run (running): {}", e);
                 });
 
                 // Register cancellation flag
@@ -122,7 +122,7 @@ impl Kernel {
                 run.duration_ms = Some(duration.as_millis() as u64);
                 run.completed_at = Some(completed_at);
                 let _ = memory.update_hand_run(&run).await.map_err(|e| {
-                    tracing::warn!("[Approval] Failed to update hand run (completed): {}", e);
+                    tracing::error!("[Approval] Failed to update hand run (completed): {}", e);
                 });
 
                 // Update approval status based on execution result