fix(ghostgram): fix Always Online + implement Ghost Mode mutual exclusion

Bugs fixed:
- Always Online had no effect after toggle — updatePresence was only called
  on app focus changes, not on settings changes. Fixed by subscribing to
  MiscSettingsManager notifications in AccountPresenceManagerImpl.

- Ghost Mode + Always Online conflict: if Ghost Mode was enabled, the early
  return in updatePresence completely blocked Always Online logic.

Changes:
- ManagedAccountPresence: priority chain Always Online > Ghost Mode > default.
  Subscribes to GhostMode/MiscSettings notifications, refreshes presence
  immediately on any change. 30s keep-alive timer for Always Online.
- GhostModeManager: enabling Ghost Mode auto-disables alwaysOnline via
  disableAlwaysOnlineForMutualExclusion(). No recursion via guard flag.
- MiscSettingsManager: enabling alwaysOnline auto-disables Ghost Mode via
  disableForMutualExclusion(). No recursion via guard flag.
- MiscController: subscribes to GhostModeManager notifications to refresh
  UI when Ghost Mode is auto-disabled by Always Online.
- GhostModeController: subscribes to MiscSettings notifications to refresh
  UI when Ghost Mode is auto-disabled by Always Online.

submodules/SettingsUI/Sources/GhostModeController.swift

@@ -300,6 +300,28 @@ public func ghostModeController(context: AccountContext) -> ViewController {
         }
     )
     
+    // Refresh UI when Always Online is enabled externally and auto-disables Ghost Mode —
+    // the isEnabled flip happens in GhostModeManager from MiscSettingsManager context,
+    // so we need to pull fresh values from the manager.
+    let miscSettingsChangedSignal: Signal<Void, NoError> = Signal { subscriber in
+        let observer = NotificationCenter.default.addObserver(
+            forName: MiscSettingsManager.settingsChangedNotification,
+            object: nil,
+            queue: .main
+        ) { _ in
+            updateState { state in
+                state.isEnabled          = GhostModeManager.shared.isEnabled
+                state.hideReadReceipts   = GhostModeManager.shared.hideReadReceipts
+                state.hideStoryViews     = GhostModeManager.shared.hideStoryViews
+                state.hideOnlineStatus   = GhostModeManager.shared.hideOnlineStatus
+                state.hideTypingIndicator = GhostModeManager.shared.hideTypingIndicator
+                state.forceOffline       = GhostModeManager.shared.forceOffline
+            }
+        }
+        return ActionDisposable { NotificationCenter.default.removeObserver(observer) }
+    }
+    let _ = miscSettingsChangedSignal.start()
+    
     let signal = combineLatest(
         context.sharedContext.presentationData,
         statePromise.get()