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/events.rs

@@ -17,8 +17,9 @@ impl EventBus {
 
     /// Publish an event
     pub fn publish(&self, event: Event) {
-        // Ignore send errors (no subscribers)
-        let _ = self.sender.send(event);
+        if let Err(e) = self.sender.send(event) {
+            tracing::debug!("Event dropped (no subscribers or channel full): {:?}", e);
+        }
     }
 
     /// Subscribe to events