refactor: unify gateway discovery on bridge

apps/macos/Sources/Clawdis/BridgeDiscoveryPreferences.swift

@@ -0,0 +1,20 @@
+import Foundation
+
+enum BridgeDiscoveryPreferences {
+    private static let preferredStableIDKey = "bridge.preferredStableID"
+
+    static func preferredStableID() -> String? {
+        let raw = UserDefaults.standard.string(forKey: self.preferredStableIDKey)
+        let trimmed = raw?.trimmingCharacters(in: .whitespacesAndNewlines)
+        return trimmed?.isEmpty == false ? trimmed : nil
+    }
+
+    static func setPreferredStableID(_ stableID: String?) {
+        let trimmed = stableID?.trimmingCharacters(in: .whitespacesAndNewlines)
+        if let trimmed, !trimmed.isEmpty {
+            UserDefaults.standard.set(trimmed, forKey: self.preferredStableIDKey)
+        } else {
+            UserDefaults.standard.removeObject(forKey: self.preferredStableIDKey)
+        }
+    }
+}