feat(apple): VoiceCatCore Swift package + XCFramework build for macOS/iOS clients

Lays the groundwork for the macOS (AppKit) and iOS (SwiftUI) clients with a shared
Swift core wrapping the C ABI, mirroring the proven Windows VoiceCat.Interop layer.

Architecture decision: macOS UI = AppKit (not SwiftUI) for the most mature VoiceOver
accessibility story — same rationale as the Windows client's WinForms-over-WinUI-3
decision. iOS stays SwiftUI. Recorded in docs/roadmap.md §2.

Build infrastructure (Phase 0):
- clients/apple/scripts/build-xcframework.sh: runs cmake --preset apple-dev, merges
  libvoicecat.a + 107 vcpkg static deps into a single ~30 MB fat static library
  (libvoicecat-fat.a) via libtool -static (SPM binary targets link one .a per slice),
  stages voicecat.h + a generated module.modulemap (module VoiceCatC) into the headers,
  runs xcodebuild -create-xcframework -> clients/apple/VoiceCatCore.xcframework.

VoiceCatCore Swift Package (Phase 1):
- Package.swift: binary target (VoiceCatCoreXCF) + library (VoiceCatCore) + test target.
- Sources/VoiceCatCore/: 7 files mirroring the C# VoiceCat.Interop patterns adapted to
  Swift native C interop — Enums (9 Swift mirrors of C enums, UInt32-backed), Config,
  Event (copies ev.text to String inside the callback — the #1 lifetime rule), Models
  (10 Swift value types), Marshaling (C arrays -> Swift + immediate vc_free_*),
  Callbacks (@convention(c) + Unmanaged.passUnretained, the Swift analog of C#'s
  [UnmanagedCallersOnly] + GCHandle), VoiceCatClient (owns vc_client* as OpaquePointer,
  all 38 C ABI functions, deinit -> vc_client_destroy then frees config CStrings, event
  delivery on main queue via coalesced DispatchQueue.main drain).

Tests — 6/6 green (swift test against a real voicecat-server):
- testConnectTofuAuthListChannelsRoundTrips, testAdminChannelCrudAccountCrudRoundTrips,
  testScreenAudioStreamStartsAndStops, testPerStreamRecvControlsRoundTrip, plus two
  static smoke tests. Catches Swift-specific interop bugs (@convention(c) callback
  lifetime, Unmanaged pointer resolution, CString memory management, enum raw-value
  bridging, struct layout) that C++ ctest cannot. C++ suite still 21/21 green.

Docs updated (house rule): tech-stack.md §2, architecture.md §4, roadmap.md M4 + §2,
clients/apple/README.md (full rewrite), PROGRESS.md, .gitignore.

clients/apple/Sources/VoiceCatCore/Event.swift

@@ -0,0 +1,61 @@
+// VoiceCatEvent — a Swift value type that is safe to hold/queue past the native callback's
+// return. This is the Swift analog of the C# client's `VoiceCatEvent` record.
+//
+// CRITICAL (voicecat.h's vc_event doc comment): the native `vc_event.text` pointer is owned
+// by the core and valid ONLY for the duration of the `on_event` callback. `from(_:)` copies
+// it to a Swift `String` immediately — never hold the raw `vc_event` across the callback
+// boundary, or `text` will be a dangling pointer by the time it's read. This is the #1
+// lifetime rule carried over from the Windows client (NativeCallbacks.cs / VoiceCatEvent.cs).
+
+import VoiceCatC
+
+/// A Swift-safe copy of a `vc_event`. Produced inside the `on_event` callback (see
+/// Callbacks.swift) — all pointer fields are converted to value types before the callback
+/// returns.
+public struct VoiceCatEvent: Sendable, Equatable {
+    public let type: VoiceCatEventType
+    public let connectionState: VoiceCatConnectionState
+    public let result: VoiceCatResult
+    public let userId: UInt32
+    public let channelId: UInt32
+    public let streamId: UInt32
+    public let textScope: VoiceCatTextScope
+    /// Generic small payload, meaning per event type. For `.serverIdentity` this is the
+    /// `VoiceCatTofuStatus`; for `.genericResult` the server error code; for `.talkState`
+    /// talking(0/1).
+    public let u32a: UInt32
+    /// Copied from the core's `vc_event.text` inside the callback. nil if the core passed NULL.
+    public let text: String?
+    public let timestampUnixMs: UInt64
+
+    /// Convenience: the TOFU status, valid when `type == .serverIdentity` (maps `u32a`).
+    public var tofuStatus: VoiceCatTofuStatus? {
+        type == .serverIdentity ? VoiceCatTofuStatus(rawValue: u32a) : nil
+    }
+
+    /// Copy a native `vc_event` into a safe Swift value. MUST be called inside the callback
+    /// while `ev.text` is still valid — `String(cString:)` copies the bytes here.
+    @inline(__always)
+    public static func from(_ ev: vc_event) -> VoiceCatEvent {
+        let text: String?
+        if let raw = ev.text {
+            text = String(cString: raw)  // copies — safe to hold past callback return
+        } else {
+            text = nil
+        }
+        // ev.result is int32_t (not vc_result) per voicecat.h — bridge via bitPattern.
+        // ev.u32a is uint32_t — matches VoiceCatTofuStatus's UInt32 raw value directly.
+        return VoiceCatEvent(
+            type: VoiceCatEventType(ev.type),
+            connectionState: VoiceCatConnectionState(ev.connection_state),
+            result: VoiceCatResult(rawValue: UInt32(bitPattern: ev.result)) ?? .internalError,
+            userId: ev.user_id,
+            channelId: ev.channel_id,
+            streamId: ev.stream_id,
+            textScope: VoiceCatTextScope(ev.text_scope),
+            u32a: ev.u32a,
+            text: text,
+            timestampUnixMs: ev.timestamp_unix_ms
+        )
+    }
+}