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.

server/src/server.cpp

@@ -205,7 +205,7 @@ void Server::stop() {
 namespace voicecat::server {
 
 int Server::run() {
-    std::fprintf(stderr, "[server] stub: VOICECAT_HAS_NET not defined (build with m1-dev)\n");
+    std::fprintf(stderr, "[server] stub: VOICECAT_HAS_NET not defined (build with dev preset)\n");
     std::printf("  server_name : %s\n", cfg_.server_name.c_str());
     std::printf("  data_dir    : %s\n", cfg_.data_dir.c_str());
     std::printf("  bind_port   : %u\n", cfg_.bind_port);