Harden PTT audio and the 1.7.1 release (#1423)

Centralize PTT and voice audio-session ownership, harden courier/bridge/outbox delivery and recovery, correct location and delivery-state races, add privacy/release metadata, and ship reproducible universal Arti slices with Release CI coverage.

Validated by the full iOS suite, repeated audio/fragment/performance regressions, BitFoundation tests, strict lint and dead-code analysis, universal iOS Release builds, and iOS/macOS archives.

bitchatTests/Mocks/MockKeychain.swift

@@ -17,6 +17,7 @@ final class MockKeychain: KeychainManagerProtocol {
     // BCH-01-009: Configurable error simulation for testing
     var simulatedReadError: KeychainReadResult?
     var simulatedSaveError: KeychainSaveResult?
+    var simulatedGenericReadError: KeychainReadResult?
 
     func saveIdentityKey(_ keyData: Data, forKey key: String) -> Bool {
         storage[key] = keyData
@@ -82,6 +83,16 @@ final class MockKeychain: KeychainManagerProtocol {
         serviceStorage[service]?[key]
     }
 
+    func loadWithResult(key: String, service: String) -> KeychainReadResult {
+        if let simulatedGenericReadError {
+            return simulatedGenericReadError
+        }
+        if let data = serviceStorage[service]?[key] {
+            return .success(data)
+        }
+        return .itemNotFound
+    }
+
     func delete(key: String, service: String) {
         serviceStorage[service]?.removeValue(forKey: key)
     }