build(scripts): add per-artifact build scripts staging into dist/

One script per main artifact, all staging into dist/ (overridable via
--dist or VOICECAT_DIST_DIR):

- build-server.sh        server-release preset -> dist/server/
- build-windows-client.sh  windows-client DLL + dotnet publish -> dist/windows-client/
- build-macos-client.sh    XCFramework + xcodebuild VoiceCatMac.app -> dist/macos-client/
- build-libs.sh           libvoicecat per platform -> dist/lib/{macos,ios*,windows}/
                         + dist/lib/VoiceCatCore.xcframework/
- build-all.sh            orchestrator (host-applicable artifacts only)
- common.sh               shared helpers: dist/VCPKG_ROOT resolution, platform
                         guards, logging, --help from header comments

Host-platform guards prevent running the wrong script on the wrong OS.
build-libs.sh and build-macos-client.sh drive the existing validated
clients/apple/scripts/build-xcframework.sh rather than duplicating it.
dist/ added to .gitignore.

scripts/build-macos-client.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+#
+# build-macos-client.sh — build the macOS AppKit client (VoiceCatMac.app) and
+# stage it into dist/macos-client/.
+#
+# Two steps:
+#   1. Build VoiceCatCore.xcframework (macOS slice) by invoking the existing
+#      clients/apple/scripts/build-xcframework.sh — that builds libvoicecat.a
+#      (apple-dev preset), merges vcpkg deps into a fat .a, and stitches the
+#      XCFramework the Swift Package consumes.
+#   2. xcodebuild the VoiceCatMac scheme into a known derivedDataPath, then
+#      copy VoiceCatMac.app into dist/macos-client/.
+#
+# Usage:
+#   scripts/build-macos-client.sh              # build + stage into ./dist/macos-client
+#   scripts/build-macos-client.sh --dist /out
+#   scripts/build-macos-client.sh --no-configure   # skip cmake configure (xcframework step)
+#   scripts/build-macos-client.sh --config Debug   # Xcode build config (default Release)
+#   scripts/build-macos-client.sh -h|--help
+#
+# macOS only. Requires VCPKG_ROOT and Xcode.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+VC_SCRIPT_NAME="build-macos-client"
+source "$SCRIPT_DIR/common.sh"
+
+DO_CONFIGURE=true
+XCODE_CONFIG="Release"
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --dist)         vc_set_dist "$2"; shift 2 ;;
+        --no-configure) DO_CONFIGURE=false; shift ;;
+        --config)       XCODE_CONFIG="$2"; shift 2 ;;
+        -h|--help)      vc_print_help "$0"; exit 0 ;;
+        *) vc_die "unknown arg: $1 (try --help)" ;;
+    esac
+done
+
+vc_require_macos
+vc_log "dist dir: $VC_DIST_DIR"
+
+vc_step "build VoiceCatCore.xcframework (macOS slice)"
+XCFW_ARGS=()
+$DO_CONFIGURE || XCFW_ARGS+=( --no-configure )
+"$VC_REPO_ROOT/clients/apple/scripts/build-xcframework.sh" "${XCFW_ARGS[@]}"
+XCFW="$VC_REPO_ROOT/clients/apple/VoiceCatCore.xcframework"
+[[ -d "$XCFW" ]] || vc_die "xcframework not found at $XCFW"
+vc_ok "xcframework ready -> $XCFW"
+
+vc_step "xcodebuild VoiceCatMac ($XCODE_CONFIG)"
+XCODEPROJ="$VC_REPO_ROOT/clients/apple/macOS/VoiceCatMac.xcodeproj"
+DERIVED="$VC_REPO_ROOT/build/macos-app"
+xcodebuild -project "$XCODEPROJ" -scheme VoiceCatMac \
+    -configuration "$XCODE_CONFIG" -derivedDataPath "$DERIVED" build
+
+APP="$DERIVED/Build/Products/$XCODE_CONFIG/VoiceCatMac.app"
+[[ -d "$APP" ]] || vc_die "VoiceCatMac.app not found at $APP"
+vc_ok "built -> $APP"
+
+vc_step "stage -> $VC_DIST_DIR/macos-client"
+STAGE="$(vc_dist_subdir macos-client)"
+cp -R "$APP" "$STAGE/"
+vc_ok "VoiceCatMac.app -> $STAGE/ ($(du -sh "$APP" | cut -f1))"
+vc_ok "done -> $STAGE"