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/Marshaling.swift

@@ -0,0 +1,107 @@
+// Marshaling — shared "walk a native array of owned-struct entries, convert to Swift value
+// types, free the native list" pattern. Identical shape for vc_device_list / vc_channel_list
+// / vc_user_list / vc_stream_summary_list / vc_account_list (all core-allocated, caller-freed
+// per voicecat.h). The matching vc_free_*_list call happens INSIDE each function here,
+// immediately after the conversion, so callers never need to remember to free anything
+// themselves. This is the Swift analog of the C# client's Marshaling.cs.
+
+import VoiceCatC
+import Foundation
+
+/// Internal marshaling helpers — convert core-allocated C arrays to Swift arrays and
+/// immediately free the native list. Not part of the public API.
+internal enum Marshaling {
+    /// Convert a nullable `const char*` to a Swift `String` (empty if NULL).
+    @inline(__always)
+    static func string(_ ptr: UnsafePointer<CChar>?) -> String {
+        guard let ptr else { return "" }
+        return String(cString: ptr)
+    }
+
+    static func devices(_ list: inout vc_device_list) -> [Device] {
+        guard let items = list.items else { vc_free_device_list(&list); return [] }
+        var result: [Device] = []
+        result.reserveCapacity(list.count)
+        for i in 0..<list.count {
+            let d = items.advanced(by: i).pointee
+            result.append(Device(id: string(d.id), name: string(d.name), isDefault: d.is_default != 0))
+        }
+        vc_free_device_list(&list)
+        return result
+    }
+
+    static func channels(_ list: inout vc_channel_list) -> [Channel] {
+        guard let items = list.items else { vc_free_channel_list(&list); return [] }
+        var result: [Channel] = []
+        result.reserveCapacity(list.count)
+        for i in 0..<list.count {
+            let c = items.advanced(by: i).pointee
+            result.append(Channel(id: c.id, parentId: c.parent_id, name: string(c.name),
+                                  topic: string(c.topic), passwordProtected: c.password_protected != 0,
+                                  maxUsers: c.max_users))
+        }
+        vc_free_channel_list(&list)
+        return result
+    }
+
+    static func users(_ list: inout vc_user_list) -> [User] {
+        guard let items = list.items else { vc_free_user_list(&list); return [] }
+        var result: [User] = []
+        result.reserveCapacity(list.count)
+        for i in 0..<list.count {
+            let u = items.advanced(by: i).pointee
+            result.append(User(id: u.id, nickname: string(u.nickname), isGuest: u.is_guest != 0,
+                               channelId: u.channel_id, selfMicMuted: u.self_mic_muted != 0,
+                               selfDeafened: u.self_deafened != 0, serverMuted: u.server_muted != 0,
+                               serverDeafened: u.server_deafened != 0))
+        }
+        vc_free_user_list(&list)
+        return result
+    }
+
+    static func streamSummaries(_ list: inout vc_stream_summary_list) -> [StreamSummary] {
+        guard let items = list.items else { vc_free_stream_summary_list(&list); return [] }
+        var result: [StreamSummary] = []
+        result.reserveCapacity(list.count)
+        for i in 0..<list.count {
+            let s = items.advanced(by: i).pointee
+            result.append(StreamSummary(streamId: s.stream_id, kind: VoiceCatStreamKind(s.kind),
+                                        label: string(s.label)))
+        }
+        vc_free_stream_summary_list(&list)
+        return result
+    }
+
+    static func accounts(_ list: inout vc_account_list) -> [Account] {
+        guard let items = list.items else { vc_free_account_list(&list); return [] }
+        var result: [Account] = []
+        result.reserveCapacity(list.count)
+        for i in 0..<list.count {
+            let a = items.advanced(by: i).pointee
+            result.append(Account(username: string(a.username), isAdmin: a.is_admin != 0,
+                                  createdAtUnixMs: a.created_at_unix_ms,
+                                  lastLoginUnixMs: a.last_login_unix_ms))
+        }
+        vc_free_account_list(&list)
+        return result
+    }
+
+    static func remoteStreamState(_ s: vc_remote_stream_state) -> RemoteStreamState {
+        RemoteStreamState(gain: s.gain, muted: s.muted != 0, noiseReduction: s.noise_reduction != 0)
+    }
+
+    static func audioConfig(_ c: vc_audio_config) -> AudioConfig {
+        AudioConfig(codec: c.codec, stereo: c.mode != 0, sampleRate: c.sample_rate,
+                    bitrateBps: c.bitrate_bps, frameMs: c.frame_ms, application: c.application,
+                    fec: c.fec != 0, expectedPacketLoss: c.expected_packet_loss,
+                    dtx: c.dtx != 0, complexity: c.complexity)
+    }
+
+    static func permissions(_ p: vc_permissions) -> Permissions {
+        Permissions(canCreateTempChannel: p.can_create_temp_channel != 0,
+                    canKick: p.can_kick != 0, canBan: p.can_ban != 0,
+                    canMoveUsers: p.can_move_users != 0,
+                    canAdminAccounts: p.can_admin_accounts != 0,
+                    isAdmin: p.is_admin != 0)
+    }
+}