重构全局 Toast 为自动消失的顶部横幅

采用全宽主色横幅居中展示文案，2.2 秒后自动隐藏，并补充定时器重置行为的测试。

Co-authored-by: Cursor <cursoragent@cursor.com>

suixinkanTests/ToastCenterTests.swift

@@ -0,0 +1,60 @@
+//
+//  ToastCenterTests.swift
+//  suixinkanTests
+//
+//  Created by Codex on 2026/6/23.
+//
+
+import XCTest
+@testable import suixinkan
+
+@MainActor
+/// 全局 Toast 状态中心测试，覆盖自动隐藏和连续展示行为。
+final class ToastCenterTests: XCTestCase {
+    /// 测试 show 会立即写入当前 Toast 文案。
+    func testShowStoresMessage() {
+        let center = ToastCenter(autoDismissNanoseconds: 100_000_000)
+
+        center.show("保存成功")
+
+        XCTAssertEqual(center.snapshotForTests, ToastSnapshot(message: "保存成功"))
+    }
+
+    /// 测试 Toast 到达自动隐藏时间后会清空文案。
+    func testToastAutoDismissesAfterDelay() async throws {
+        let center = ToastCenter(autoDismissNanoseconds: 60_000_000)
+
+        center.show("保存成功")
+        try await Task.sleep(nanoseconds: 90_000_000)
+
+        XCTAssertEqual(center.snapshotForTests, ToastSnapshot(message: nil))
+    }
+
+    /// 测试连续 show 会覆盖旧文案，并重新计算自动隐藏时间。
+    func testRepeatedShowResetsAutoDismissTimer() async throws {
+        let center = ToastCenter(autoDismissNanoseconds: 100_000_000)
+
+        center.show("第一条")
+        try await Task.sleep(nanoseconds: 70_000_000)
+        center.show("第二条")
+        try await Task.sleep(nanoseconds: 60_000_000)
+
+        XCTAssertEqual(center.snapshotForTests, ToastSnapshot(message: "第二条"))
+
+        try await Task.sleep(nanoseconds: 70_000_000)
+        XCTAssertEqual(center.snapshotForTests, ToastSnapshot(message: nil))
+    }
+
+    /// 测试手动 dismiss 会立即清空文案，并取消当前自动隐藏任务。
+    func testDismissClearsMessageImmediately() async throws {
+        let center = ToastCenter(autoDismissNanoseconds: 100_000_000)
+
+        center.show("保存成功")
+        center.dismiss()
+
+        XCTAssertEqual(center.snapshotForTests, ToastSnapshot(message: nil))
+
+        try await Task.sleep(nanoseconds: 130_000_000)
+        XCTAssertEqual(center.snapshotForTests, ToastSnapshot(message: nil))
+    }
+}