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.

clients/apple/README.md

@@ -17,3 +17,40 @@ Planned shape (see [`docs/architecture.md`](../../docs/architecture.md) §4 and
   state via an **App Group** ([`docs/voice.md`](../../docs/voice.md) §9).
 
 Nothing here yet — the core must reach M2 (working voice) before the GUI is worth building.
+
+## Building the core for Apple platforms (scaffolding)
+
+The CMake presets `apple-dev`, `apple-ios`, and `apple-ios-sim` produce static `libvoicecat.a`
+slices for the Swift Package / XCFramework. They are **scaffolding** — not yet CI-validated.
+Build on macOS (they won't work on Windows/Linux):
+
+```bash
+# Prerequisites: VCPKG_ROOT set, Xcode + iOS SDK installed
+export VCPKG_ROOT=/path/to/vcpkg
+
+# macOS slice (arm64-osx on Apple Silicon, x64-osx on Intel)
+cmake --preset apple-dev && cmake --build --preset apple-dev
+# → build/apple-dev/lib/libvoicecat.a
+
+# iOS device slice
+cmake --preset apple-ios && cmake --build --preset apple-ios
+# → build/apple-ios/lib/libvoicecat.a
+
+# iOS simulator slice
+cmake --preset apple-ios-sim && cmake --build --preset apple-ios-sim
+# → build/apple-ios-sim/lib/libvoicecat.a
+```
+
+The three `.a` files are then stitched into an XCFramework:
+
+```bash
+xcodebuild -create-xcframework \
+  -library build/apple-dev/lib/libvoicecat.a -headers core/include \
+  -library build/apple-ios/lib/libvoicecat.a -headers core/include \
+  -library build/apple-ios-sim/lib/libvoicecat.a -headers core/include \
+  -output build/VoiceCatCore.xcframework
+```
+
+The XCFramework is then consumed by the Swift Package as a binary target. Actual
+`AVAudioSession` integration, `Info.plist` mic permission, ReplayKit extension, and SwiftUI
+UI work are tracked as follow-up tasks — the presets exist so the build entry point is ready.