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.

tests/CMakeLists.txt

@@ -6,7 +6,7 @@ target_link_libraries(test_smoke PRIVATE voicecat::voicecat)
 target_compile_features(test_smoke PRIVATE cxx_std_20)
 add_test(NAME smoke COMMAND test_smoke)
 
-# frame_codec has no third-party deps; runs under both dev and m1-dev.
+# frame_codec has no third-party deps; runs under both skeleton and dev.
 # Needs core/src on the include path to reach internal headers (protocol/, session/, etc.).
 add_executable(test_frame_codec test_frame_codec.cpp)
 target_link_libraries(test_frame_codec PRIVATE voicecat::voicecat)