build(cmake): clean up presets, add release/apple presets, cross-platform triplets

Rationalize the preset set to match the project's actual state (past M5):
- Rename dev->skeleton (no-deps stub smoke), m1-dev->dev (default dev preset)
- Drop m2-dev (cache-identical to m1-dev)
- Add release preset (optimized + tests on, symbols kept)
- Strip server-release binaries (-s linker flag)
- Add apple-dev/apple-ios/apple-ios-sim scaffolding presets for XCFramework

Add cmake/voicecat-toolchain.cmake wrapper that auto-resolves the vcpkg
triplet from the host platform (x64-mingw-static/x64-linux/arm64-osx) so
the main presets work on Windows/Linux/macOS without per-OS variants.

Update all docs (building.md, CLAUDE.md, README.md, AGENTS.md, deployment.md,
tech-stack.md, client READMEs) and stale preset-name references in code
comments. No C++ behavior changes — the core was already portable.

clients/windows/README.md

@@ -16,8 +16,8 @@ WinForms (.NET 10 LTS) UI over `voicecat.dll` (MinGW-built `libvoicecat` shared
 ### 1. Build the server (for testing)
 
 ```powershell
-cmake --preset m1-dev
-cmake --build --preset m1-dev --target voicecat-server
+cmake --preset dev
+cmake --build --preset dev --target voicecat-server
 ```
 
 ### 2. Build the DLL
@@ -53,7 +53,7 @@ into the output directory automatically on every build.
 
 ```powershell
 # Terminal 1 — start the server
-./build/m1-dev/bin/voicecat-server.exe --name "My Server"
+./build/dev/bin/voicecat-server.exe --name "My Server"
 
 # Terminal 2 — launch the client
 dotnet run --project clients/windows/VoiceCat.App/VoiceCat.App.csproj