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.

core/src/voicecat.cpp

@@ -3,8 +3,8 @@
  *
  * Lifecycle (create/destroy) and trivial accessors are always real. Everything else below
  * just delegates to vc_client (core/src/core/client.cpp): under VOICECAT_HAS_NET
- * (`m1-dev`/`server-release` — see docs/building.md) that's the real M1–M3 implementation;
- * under the no-deps `dev` preset, client.cpp's `#else` branch returns VC_ERR_NOT_IMPLEMENTED
+ * (`dev`/`release`/`server-release` — see docs/building.md) that's the real M1–M3 implementation;
+ * under the no-deps `skeleton` preset, client.cpp's `#else` branch returns VC_ERR_NOT_IMPLEMENTED
  * for all of it, to keep that skeleton build green.
  */
 #include "voicecat.h"