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.

PROGRESS.md

@@ -10,6 +10,63 @@ up instantly. Newest status at the top.
 
 ## ▶ Where we left off / next action
 
+- **Done:** **macOS/iOS Swift core — `VoiceCatCore` package + tests** (2026-06-18). The
+  shared Swift core for the macOS (AppKit) and iOS (SwiftUI) clients is built and verified.
+  This is the foundation that both platform UIs will build on — mirrors the Windows client's
+  proven `VoiceCat.Interop` layer using Swift-native C interop.
+  - **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 and
+    `docs/tech-stack.md` §2.
+  - **`VoiceCatCore` Swift Package** (`clients/apple/Package.swift`): binary target
+    (`VoiceCatCoreXCF` → `VoiceCatCore.xcframework`) + library target (`VoiceCatCore` — the
+    Swift wrapper) + test target (`VoiceCatCoreTests`). 7 source files:
+    `Enums.swift` (Swift mirrors of the 9 C enums), `Config.swift`, `Event.swift`
+    (copies `ev.text` to `String` inside the callback — the #1 lifetime rule),
+    `Models.swift` (Channel/User/Stream/Device/Permissions/Account/AudioConfig/…),
+    `Marshaling.swift` (C arrays → Swift arrays + immediate `vc_free_*`),
+    `Callbacks.swift` (`@convention(c)` + `Unmanaged.passUnretained` — the Swift analog of
+    C#'s `[UnmanagedCallersOnly]` + `GCHandle`), `VoiceCatClient.swift` (owns `vc_client*`,
+    all 38 C functions, `deinit` → `vc_client_destroy` then frees config CStrings, event
+    delivery on `@MainActor` via coalesced `DispatchQueue.main` drain).
+  - **`build-xcframework.sh`** (`clients/apple/scripts/`): 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`, stages `voicecat.h` + a generated
+    `module.modulemap` (`module VoiceCatC { header "voicecat.h" }`) into the XCFramework
+    headers, runs `xcodebuild -create-xcframework` → `clients/apple/VoiceCatCore.xcframework`.
+    The fat library is needed because SPM binary targets link ONE `.a` per slice — without
+    it, the final executable gets undefined-symbol errors for protobuf/mbedtls/sodium/opus/…
+    (the Apple equivalent of how the Windows client ships a single `voicecat.dll` with all
+    deps statically linked).
+  - **Tests — 6/6 green:** `swift test` against a real `voicecat-server` (built by
+    `cmake --preset dev`). Tests mirror the C# `VoiceCat.Interop.Tests`:
+    `testVersionStringIsNonEmpty`, `testResultStringRoundTrips`,
+    `testConnectTofuAuthListChannelsRoundTrips` (connect → TOFU → confirm → guest auth →
+    channels → permissions → guest ListAccounts rejected),
+    `testAdminChannelCrudAccountCrudRoundTrips` (admin auth → channel CRUD → account CRUD),
+    `testScreenAudioStreamStartsAndStops` (screen-audio stream lifecycle through Swift),
+    `testPerStreamRecvControlsRoundTrip` (two clients, per-stream gain/mute/NR round-trip).
+    Catches Swift-specific interop bugs (`@convention(c)` callback lifetime, `Unmanaged`
+    pointer resolution, CString memory management, enum raw-value bridging, struct layout)
+    that C++ ctest can't.
+  - **Key C interop discoveries:** (1) Swift imports `vc_client*` (incomplete C struct) as
+    `OpaquePointer?`, not a named type — `private var handle: OpaquePointer?`. (2) C enums
+    are imported as `UInt32`-backed (not `Int32`) — all Swift enum mirrors use `UInt32`;
+    `vc_event.result` is `int32_t` (signed), bridged via `UInt32(bitPattern:)`. (3) Swift
+    auto-marshals `String` to `const char*` for function params, but NOT for C struct fields
+    — `vc_stream_desc`/`vc_channel_info` string fields need `strdup` + `defer { free }`.
+    (4) `selfPointer` must be a computed property (not stored) to break the circular init
+    dependency (`Unmanaged.passUnretained(self)` needs `self` fully initialized, but stored
+    properties must be set first).
+  - **Docs updated:** `docs/tech-stack.md` §2 (AppKit macOS / SwiftUI iOS / shared
+    `VoiceCatCore` package / fat static lib), `docs/architecture.md` §4 (Swift binding
+    notes), `docs/roadmap.md` M4 + §2 (AppKit decision recorded), `clients/apple/README.md`
+    (full rewrite), `PROGRESS.md` (this entry), `.gitignore` (XCFramework + SPM artifacts).
+  - **Next:** macOS AppKit app (`clients/apple/macOS/`) — connect dialog, saved-server list
+    (Keychain), TOFU identity dialog, main window (NSOutlineView + NSTableView + NSTextView
+    + activity log), voice controls, per-user tuning, full VoiceOver accessibility. Mirrors
+    the Windows `VoiceCat.App` feature set.
+
 - **Done:** **macOS port — `dev` + `apple-dev` presets validated** (2026-06-18). The core,
   server, tools, and tests now build and run on macOS (Apple Silicon, macOS 26.5, Apple clang
   21). This lays the groundwork for the macOS/iOS Swift client. Three real bugs found and