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.

localPackages/BitFoundation/Sources/BitFoundation/KeychainManagerProtocol.swift

@@ -32,12 +32,27 @@ public protocol KeychainManagerProtocol {
     func save(key: String, data: Data, service: String, accessible: CFString?)
     /// Load data from a custom service
     func load(key: String, service: String) -> Data?
+    /// Load data from a custom service while preserving Keychain status.
+    /// Callers that own encrypted files need to distinguish a missing key
+    /// from a temporarily inaccessible key before replacing those files.
+    func loadWithResult(key: String, service: String) -> KeychainReadResult
     /// Delete data from a custom service
     func delete(key: String, service: String)
     /// Delete every item stored under a custom service
     func deleteAll(service: String)
 }
 
+public extension KeychainManagerProtocol {
+    /// Source-compatible fallback for lightweight/test implementations. The
+    /// production manager overrides this with the underlying OSStatus.
+    func loadWithResult(key: String, service: String) -> KeychainReadResult {
+        if let data = load(key: key, service: service) {
+            return .success(data)
+        }
+        return .itemNotFound
+    }
+}
+
 // MARK: - Keychain Error Types
 // BCH-01-009: Proper error classification to distinguish expected states from critical failures