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.

cmake/voicecat-toolchain.cmake

@@ -0,0 +1,72 @@
+# cmake/voicecat-toolchain.cmake — vcpkg toolchain wrapper with auto-triplet.
+#
+# Wraps vcpkg's toolchain to auto-resolve VCPKG_HOST_TRIPLET and VCPKG_TARGET_TRIPLET
+# from the host platform, so the main presets (dev, release, server-release) build on
+# Windows/MinGW, Linux, and macOS without per-OS preset variants.
+#
+# Triplet mapping (auto):
+#   Windows       → x64-mingw-static   (the project's toolchain is MSYS2/UCRT64 — see
+#                                       clients/windows/README.md; MSVC users must set
+#                                       VCPKG_TARGET_TRIPLET=x64-windows explicitly)
+#   Linux  x64    → x64-linux
+#   Linux  arm64  → arm64-linux
+#   macOS  arm64  → arm64-osx          (Apple Silicon)
+#   macOS  x64    → x64-osx            (Intel)
+#
+# Cross-compile presets (apple-ios, apple-ios-sim) set VCPKG_TARGET_TRIPLET explicitly
+# in their cacheVariables; the DEFINED guards below preserve those. VCPKG_HOST_TRIPLET
+# is always the host's (e.g. arm64-osx when cross-compiling iOS on Apple Silicon).
+#
+# Requires VCPKG_ROOT in the environment (set by the inheriting preset).
+
+# ── Host triplet (the platform running vcpkg / the build) ─────────────────────
+if(NOT DEFINED VCPKG_HOST_TRIPLET)
+    if(CMAKE_HOST_SYSTEM_NAME STREQUAL "Windows")
+        set(_voicecat_host "x64-mingw-static")
+    elseif(CMAKE_HOST_SYSTEM_NAME STREQUAL "Linux")
+        if(CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "aarch64|arm64")
+            set(_voicecat_host "arm64-linux")
+        else()
+            set(_voicecat_host "x64-linux")
+        endif()
+    elseif(CMAKE_HOST_SYSTEM_NAME STREQUAL "Darwin")
+        if(CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "aarch64|arm64")
+            set(_voicecat_host "arm64-osx")
+        else()
+            set(_voicecat_host "x64-osx")
+        endif()
+    endif()
+    if(_voicecat_host)
+        set(VCPKG_HOST_TRIPLET "${_voicecat_host}" CACHE STRING "vcpkg host triplet (auto-resolved)")
+    endif()
+    unset(_voicecat_host)
+endif()
+
+# ── Target triplet (the platform being built for) ─────────────────────────────
+# Auto-resolve only when not explicitly set. Cross-compile presets (apple-ios,
+# apple-ios-sim) set VCPKG_TARGET_TRIPLET in their cacheVariables; the DEFINED
+# guard preserves those so they win over the auto-detection.
+if(NOT DEFINED VCPKG_TARGET_TRIPLET)
+    if(CMAKE_HOST_SYSTEM_NAME STREQUAL "Windows")
+        set(_voicecat_target "x64-mingw-static")
+    elseif(CMAKE_HOST_SYSTEM_NAME STREQUAL "Linux")
+        if(CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "aarch64|arm64")
+            set(_voicecat_target "arm64-linux")
+        else()
+            set(_voicecat_target "x64-linux")
+        endif()
+    elseif(CMAKE_HOST_SYSTEM_NAME STREQUAL "Darwin")
+        if(CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "aarch64|arm64")
+            set(_voicecat_target "arm64-osx")
+        else()
+            set(_voicecat_target "x64-osx")
+        endif()
+    endif()
+    if(_voicecat_target)
+        set(VCPKG_TARGET_TRIPLET "${_voicecat_target}" CACHE STRING "vcpkg target triplet (auto-resolved)")
+    endif()
+    unset(_voicecat_target)
+endif()
+
+# ── Hand off to the real vcpkg toolchain ──────────────────────────────────────
+include("$ENV{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake")