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>

suixinkan/UI/Loading/GlobalLoadingManager.swift

@@ -0,0 +1,74 @@
+//
+//  GlobalLoadingManager.swift
+//  suixinkan
+//
+
+import UIKit
+
+/// 全局 Loading 管理器，对齐 Android `GlobalLoadingManager`。
+@MainActor
+final class GlobalLoadingManager {
+
+    static let shared = GlobalLoadingManager()
+
+    private var loadingCount = 0
+    private weak var hostWindow: UIWindow?
+    private var overlayView: GlobalLoadingOverlayView?
+
+    private init() {}
+
+    /// 当前是否正在展示 Loading。
+    var isShowing: Bool {
+        loadingCount > 0
+    }
+
+    /// 增加 Loading 引用计数并展示遮罩。
+    func show() {
+        loadingCount += 1
+        guard loadingCount == 1 else { return }
+        attachOverlayIfNeeded()
+        overlayView?.present()
+    }
+
+    /// 减少 Loading 引用计数，归零后立即隐藏遮罩。
+    func hide() {
+        guard loadingCount > 0 else { return }
+        loadingCount -= 1
+        guard loadingCount == 0 else { return }
+        overlayView?.dismiss()
+        overlayView?.removeFromSuperview()
+    }
+
+    /// 强制关闭所有 Loading。
+    func hideAll() {
+        loadingCount = 0
+        overlayView?.dismiss()
+        overlayView?.removeFromSuperview()
+    }
+
+    private func attachOverlayIfNeeded() {
+        guard let window = keyWindow else { return }
+        hostWindow = window
+
+        if overlayView == nil {
+            let overlay = GlobalLoadingOverlayView(frame: window.bounds)
+            overlay.autoresizingMask = [.flexibleWidth, .flexibleHeight]
+            overlay.isHidden = true
+            overlayView = overlay
+        }
+
+        guard let overlayView else { return }
+        if overlayView.superview !== window {
+            overlayView.removeFromSuperview()
+            window.addSubview(overlayView)
+        }
+        window.bringSubviewToFront(overlayView)
+    }
+
+    private var keyWindow: UIWindow? {
+        UIApplication.shared.connectedScenes
+            .compactMap { $0 as? UIWindowScene }
+            .flatMap(\.windows)
+            .first { $0.isKeyWindow }
+    }
+}