docs: add Windows + macOS client build commands to building.md

Add §7 (Windows client: dotnet build) and §8 (macOS client: XCFramework
+ xcodebuild) with the full build/run commands for each client platform.
Also add a quick-navigation table at the top of the doc.

docs/building.md

@@ -7,6 +7,16 @@ This doc explains what each CMake preset in [`CMakePresets.json`](../CMakePreset
 the missing middle: *how the presets relate to each other*, *which platform each targets*,
 and *how to drive the binaries by hand*.
 
+**Quick navigation:**
+
+| What you want to build | Section | Key command |
+|------------------------|---------|-------------|
+| Server + `vccli` + tests (all platforms) | [§3](#3-build--test-the-loop-youll-run-constantly) | `cmake --preset dev && cmake --build --preset dev && ctest --preset dev` |
+| Production server (stripped, no tests) | [§5](#5-server-release-production-shaped-build) | `cmake --preset server-release && cmake --build --preset server-release` |
+| Windows client (C# / WinForms) | [§7](#7-windows-client-c--winforms) | `dotnet build clients/windows/VoiceCat.slnx` |
+| macOS client (AppKit) | [§8](#8-macos-client-appkit) | `xcodebuild -project clients/apple/macOS/VoiceCatMac.xcodeproj -scheme VoiceCatMac build` |
+| Swift core + tests | [§8](#8-macos-client-appkit) | `cd clients/apple && swift test` |
+
 ## 1. What each preset is for
 
 | Preset | Binary dir | Deps | Build type | Server | Tools | Tests | Strip | Platform | What it's for |
@@ -234,3 +244,106 @@ The three `.a` files are then stitched into an XCFramework via `xcodebuild
 planned workflow). Actual XCFramework stitching, `AVAudioSession` integration, and iOS
 UI work are tracked as follow-up tasks — the presets exist so the build entry point is ready
 when that work starts.
+
+## 7. Windows client (C# / WinForms)
+
+The Windows client is a .NET 10 WinForms app that loads `voicecat.dll` (the MinGW-built
+shared library from the `windows-client` preset) via P/Invoke. Full details in
+[`clients/windows/README.md`](../clients/windows/README.md).
+
+**Prerequisites:** .NET SDK 10, MinGW-w64 / MSYS2 UCRT64 (GCC 13+), vcpkg.
+
+### Build the DLL
+
+```powershell
+cmake --preset windows-client
+cmake --build --preset windows-client
+# → build/windows-client/bin/voicecat.dll
+```
+
+### Build the C# solution
+
+```powershell
+cd clients/windows
+dotnet build VoiceCat.slnx
+```
+
+`Directory.Build.props` copies `voicecat.dll` into the output directory automatically.
+
+### Run the app
+
+```powershell
+# Terminal 1 — start the server (built with the dev preset)
+./build/dev/bin/voicecat-server.exe --name "My Server"
+
+# Terminal 2 — launch the client
+dotnet run --project clients/windows/VoiceCat.App/VoiceCat.App.csproj
+```
+
+### Run the C# interop tests
+
+```powershell
+dotnet test clients/windows/VoiceCat.slnx
+```
+
+## 8. macOS client (AppKit)
+
+The macOS client is an Xcode project (AppKit / Swift) that links `libvoicecat` via the
+`VoiceCatCore` Swift Package, which consumes a binary XCFramework target. Full details in
+[`clients/apple/README.md`](../clients/apple/README.md).
+
+**Prerequisites:** Xcode, vcpkg (`VCPKG_ROOT` set), macOS 14+ (deployment target).
+
+### Build the XCFramework
+
+The XCFramework is a local build artifact (gitignored, like the Windows DLL). It bundles
+`libvoicecat.a` + all vcpkg static deps into a single fat `.a` per slice, plus staged
+headers with a module map so Swift gets `import VoiceCatC`.
+
+```bash
+# macOS slice only (default, validated)
+clients/apple/scripts/build-xcframework.sh
+# → clients/apple/VoiceCatCore.xcframework/
+
+# All 3 slices (macOS + iOS device + iOS sim — iOS still scaffolding)
+clients/apple/scripts/build-xcframework.sh --all
+```
+
+The script runs `cmake --preset apple-dev` + `cmake --build --preset apple-dev` internally,
+then merges vcpkg's static deps with `libtool -static` and stitches the XCFramework with
+`xcodebuild -create-xcframework`.
+
+### Build the Swift core (SPM)
+
+```bash
+cd clients/apple
+swift build        # builds VoiceCatCore library
+swift test         # 6 smoke tests against a real voicecat-server
+```
+
+`swift test` requires the `dev` CMake preset to be built
+(`build/dev/bin/voicecat-server` + `voicecat-admin`).
+
+### Build the macOS app (Xcode)
+
+```bash
+xcodebuild -project clients/apple/macOS/VoiceCatMac.xcodeproj \
+    -scheme VoiceCatMac -configuration Debug build
+# → ~/Library/Developer/Xcode/DerivedData/VoiceCatMac-*/Build/Products/Debug/VoiceCatMac.app
+```
+
+Or open the project in Xcode and build from the UI:
+
+```bash
+open clients/apple/macOS/VoiceCatMac.xcodeproj
+```
+
+### Run the app
+
+```bash
+# Terminal 1 — start the server (built with the dev preset)
+./build/dev/bin/voicecat-server --name "My Server"
+
+# Terminal 2 — launch the client
+open ~/Library/Developer/Xcode/DerivedData/VoiceCatMac-*/Build/Products/Debug/VoiceCatMac.app
+```