Add Lottie global loading overlay and fix stuck loading states.

Replace per-VC activity indicators with a ref-counted GlobalLoadingManager, and resolve duplicate show/hide calls on Profile, Statistics, and Home tabs.

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

suixinkanTests/GlobalLoadingManagerTests.swift

@@ -0,0 +1,54 @@
+//
+//  GlobalLoadingManagerTests.swift
+//  suixinkanTests
+//
+
+import XCTest
+@testable import suixinkan
+
+@MainActor
+/// 全局 Loading 管理器测试。
+final class GlobalLoadingManagerTests: XCTestCase {
+
+    override func tearDown() {
+        GlobalLoadingManager.shared.hideAll()
+        super.tearDown()
+    }
+
+    func testShowAndHideToggleVisibilityState() {
+        let manager = GlobalLoadingManager.shared
+        XCTAssertFalse(manager.isShowing)
+
+        manager.show()
+        XCTAssertTrue(manager.isShowing)
+
+        manager.hide()
+        XCTAssertFalse(manager.isShowing)
+    }
+
+    func testNestedShowRequiresMatchingHideCount() {
+        let manager = GlobalLoadingManager.shared
+
+        manager.show()
+        manager.show()
+        XCTAssertTrue(manager.isShowing)
+
+        manager.hide()
+        XCTAssertTrue(manager.isShowing)
+
+        manager.hide()
+        XCTAssertFalse(manager.isShowing)
+    }
+
+    func testHideAllResetsNestedCount() {
+        let manager = GlobalLoadingManager.shared
+
+        manager.show()
+        manager.show()
+        manager.hideAll()
+        XCTAssertFalse(manager.isShowing)
+
+        manager.hide()
+        XCTAssertFalse(manager.isShowing)
+    }
+}