Fix brightness HUD not working on macOS Tahoe 26.5

The brightness HUD broke on Tahoe because Apple deprecated/changed the
DisplayServices private framework and stopped posting the BezelEngine
distributed notifications that Atoll relied on for change detection.

This commit:
- Adds CoreBrightnessDisplayClient using Apple's CoreBrightness framework
  (mirrors the existing KeyboardBrightnessClient pattern) as the primary
  brightness read/write path
- Falls back gracefully to DisplayServices then IODisplay if CoreBrightness
  is unavailable
- Adds a lightweight polling fallback (150ms) so the HUD fires even when
  no distributed notifications are posted (Control Center, Touch Bar, auto-
  brightness changes)
- Registers the new com.apple.CoreBrightness.DisplayBrightnessChanged
  notification
- Fixes deprecated kIOMasterPortDefault → kIOMainPortDefault in
  SystemDisplayManager.swift

Fixes #452

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

DynamicIsland/helpers/CoreBrightnessDisplayClient.swift

@@ -0,0 +1,82 @@
+/*
+ * Atoll (DynamicIsland)
+ * Copyright (C) 2024-2026 Atoll Contributors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import Foundation
+import ObjectiveC.runtime
+
+final class CoreBrightnessDisplayClient {
+    static let shared = CoreBrightnessDisplayClient()
+
+    private static let builtInDisplayID: UInt64 = 0
+
+    private var clientInstance: NSObject?
+    private let getSelector = NSSelectorFromString("brightnessForDisplay:")
+    private let setSelector = NSSelectorFromString("setBrightness:forDisplay:")
+    private let notificationSelector = NSSelectorFromString("setNotificationBlock:")
+
+    var onBrightnessChange: ((Float) -> Void)?
+    private var available = false
+
+    private init() {
+        var loaded = false
+        let bundlePaths = [
+            "/System/Library/PrivateFrameworks/CoreBrightness.framework",
+            "/System/Library/PrivateFrameworks/CoreBrightness.framework/CoreBrightness"
+        ]
+        for path in bundlePaths where !loaded {
+            if let bundle = Bundle(path: path) {
+                loaded = bundle.load()
+            }
+        }
+        guard loaded, let cls = NSClassFromString("DisplayBrightnessClient") as? NSObject.Type else {
+            NSLog("⚠️ CoreBrightnessDisplayClient: DisplayBrightnessClient class not found")
+            return
+        }
+        clientInstance = cls.init()
+        available = clientInstance != nil
+    }
+
+    var isAvailable: Bool { available }
+
+    func currentBrightness() -> Float? {
+        guard let clientInstance,
+              let getter: BrightnessGetter = methodIMP(on: clientInstance, selector: getSelector, as: BrightnessGetter.self)
+        else { return nil }
+        let value = getter(clientInstance, getSelector, Self.builtInDisplayID)
+        guard value >= 0, value <= 1 else { return nil }
+        return value
+    }
+
+    func setBrightness(_ value: Float) -> Bool {
+        guard let clientInstance,
+              let setter: BrightnessSetter = methodIMP(on: clientInstance, selector: setSelector, as: BrightnessSetter.self)
+        else { return false }
+        return setter(clientInstance, setSelector, value, Self.builtInDisplayID).boolValue
+    }
+
+    private typealias BrightnessGetter = @convention(c) (NSObject, Selector, UInt64) -> Float
+    private typealias BrightnessSetter = @convention(c) (NSObject, Selector, Float, UInt64) -> ObjCBool
+
+    private func methodIMP<T>(on object: NSObject, selector: Selector, as type: T.Type) -> T? {
+        guard let cls = object_getClass(object),
+              let method = class_getInstanceMethod(cls, selector)
+        else { return nil }
+        let imp = method_getImplementation(method)
+        return unsafeBitCast(imp, to: T.self)
+    }
+}