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.

CLAUDE.md

@@ -4,11 +4,10 @@ Auto-loaded each session. This is the **map**: build commands, architecture at a
 where everything is. For the *working method* read [`AGENTS.md`](AGENTS.md); for *what's done
 and what's next* read [`PROGRESS.md`](PROGRESS.md); for *design* read [`docs/`](docs/).
 
-> **One-line status:** M4 (Windows WinForms C# client) is complete — connect, saved servers,
-> TOFU identity pinning, channel tree, voice (VAD/PTT/always-on + VAD threshold slider +
-> per-user tuning), text chat, device pickers, level meters. `ctest --preset m1-dev` green —
-> 14/14 tests. `dotnet build` green — 0 warnings. macOS/iOS Swift client and M5 (moderation)
-> are next. See [`PROGRESS.md`](PROGRESS.md).
+> **One-line status:** M5 (moderation & admin UI) is complete — permissions, kick/ban/move,
+> server-mute, channel CRUD, in-app account management, disconnect/keepalive/reaper. Windows
+> WinForms C# client is shipped (M4). `ctest --preset dev` green — 21/21 tests. macOS/iOS
+> Swift client is next. See [`PROGRESS.md`](PROGRESS.md).
 
 VoiceCat = self-hosted native voice & text chat (TeamSpeak/Mumble-style). Plain TCP (control)
 + UDP (media), no WebRTC, encrypted by default. A shared C++ core (`libvoicecat`) drives
@@ -18,15 +17,16 @@ native clients (Swift on macOS/iOS, C# on Windows) and the server.
 
 ## Build & test commands
 
-The **M0 skeleton builds with no third-party dependencies** — just CMake + Ninja + a C++20
-compiler. Deps (vcpkg) are off until a subsystem needs them.
+The default development preset is **`dev`** — it builds everything (server + tools + tests)
+with real vcpkg deps. The `skeleton` preset (no deps, stubs only) is a fast smoke check; see
+[`docs/building.md`](docs/building.md) for the full preset matrix.
 
 ```bash
-# Configure + build the skeleton (default; no vcpkg needed)
+# Configure + build (default development preset; needs VCPKG_ROOT)
 cmake --preset dev
 cmake --build --preset dev
 
-# Run the tests (behavior smoke test today; grows per milestone)
+# Run the tests (21 behavior tests — grows per milestone)
 ctest --preset dev                      # or: ctest --test-dir build/dev --output-on-failure
 
 # Run the binaries (Windows adds .exe; Linux/macOS no extension)
@@ -43,14 +43,26 @@ rm -rf build/dev                         # nuke; or:
 cmake --build --preset dev --target clean
 ```
 
-When you start a subsystem that needs real libraries (mbedTLS, libsodium, opus, protobuf, …),
-turn vcpkg deps on:
+Other presets (see [`docs/building.md`](docs/building.md) for full detail):
+
+```bash
+cmake --preset skeleton                  # no-deps stub smoke (no VCPKG_ROOT needed) — 2 tests
+cmake --preset release                   # optimized + tests on, symbols kept (profile/debug-friendly)
+cmake --preset server-release            # optimized + stripped, no tests (deployment-shaped)
+cmake --preset windows-client            # voicecat.dll for the C# WinForms client (Windows only)
+cmake --preset apple-dev                 # libvoicecat.a for macOS Swift Package (scaffolding, macOS only)
+```
+
+Vcpkg triplet is auto-resolved from the host platform by
+[`cmake/voicecat-toolchain.cmake`](cmake/voicecat-toolchain.cmake) — `x64-mingw-static` on
+Windows, `x64-linux` on Linux, `arm64-osx` on Apple Silicon. See docs/building.md §1
+"Platform matrix" for details.
+
+One-time vcpkg setup:
 
 ```bash
 # one-time: git clone https://github.com/microsoft/vcpkg && ./vcpkg/bootstrap-vcpkg.sh  (.bat on Windows)
 export VCPKG_ROOT=/path/to/vcpkg         # works on Linux / macOS / Windows
-cmake --preset server-release            # auto-installs deps pinned in vcpkg.json
-cmake --build --preset server-release
 ```
 
 Other useful toggles (pass with `-D` at configure time):