Add Mac build pipeline with Sparkle auto-updates (#5193)

- Unity Mac build scripts (build_mac.sh, build_unity_mac.sh)
- Code signing with Developer ID certificate
- Apple notarization for Gatekeeper compliance
- Sparkle framework injection for delta auto-updates
- Go build handler for S3 upload and appcast.xml generation
- Update InvitationCodeManager.cs for Mac platform paths
- GitHub Actions workflow triggered on main branch pushes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

scripts/codesign_mac_app.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+#
+# Code sign a macOS .app bundle for distribution
+# Usage: codesign_mac_app.sh <app_path> [entitlements_path]
+#
+# Environment variables:
+#   SIGNING_IDENTITY - The signing identity (default: "Developer ID Application")
+#   KEYCHAIN_PASSWORD - Password to unlock the build keychain (optional)
+
+set -euxo pipefail
+
+APP_PATH="$1"
+ENTITLEMENTS_PATH="${2:-}"
+SIGNING_IDENTITY="${SIGNING_IDENTITY:-Developer ID Application}"
+
+if [ ! -d "$APP_PATH" ]; then
+    echo "ERROR: App not found at $APP_PATH"
+    exit 1
+fi
+
+# Unlock keychain if password provided
+if [ -n "${KEYCHAIN_PASSWORD:-}" ]; then
+    security unlock-keychain -p "$KEYCHAIN_PASSWORD" build.keychain || true
+fi
+
+echo "=== Signing nested components first ==="
+
+# Sign all dylibs
+find "$APP_PATH" -name "*.dylib" -print0 | while IFS= read -r -d '' item; do
+    echo "Signing dylib: $item"
+    codesign --force --verify --verbose --timestamp --options runtime \
+        --sign "$SIGNING_IDENTITY" "$item"
+done
+
+# Sign all bundles (plugins)
+find "$APP_PATH" -name "*.bundle" -print0 | while IFS= read -r -d '' item; do
+    echo "Signing bundle: $item"
+    codesign --force --verify --verbose --timestamp --options runtime \
+        --sign "$SIGNING_IDENTITY" "$item"
+done
+
+# Sign all frameworks
+find "$APP_PATH" -name "*.framework" -print0 | while IFS= read -r -d '' item; do
+    echo "Signing framework: $item"
+    codesign --force --verify --verbose --timestamp --options runtime \
+        --sign "$SIGNING_IDENTITY" "$item"
+done
+
+echo "=== Signing main app bundle ==="
+
+if [ -n "$ENTITLEMENTS_PATH" ] && [ -f "$ENTITLEMENTS_PATH" ]; then
+    echo "Using entitlements: $ENTITLEMENTS_PATH"
+    codesign --force --verify --verbose --timestamp --options runtime \
+        --entitlements "$ENTITLEMENTS_PATH" \
+        --sign "$SIGNING_IDENTITY" "$APP_PATH"
+else
+    codesign --force --verify --verbose --timestamp --options runtime \
+        --sign "$SIGNING_IDENTITY" "$APP_PATH"
+fi
+
+echo "=== Verifying signature ==="
+codesign --verify --verbose=4 "$APP_PATH"
+
+echo "=== Checking Gatekeeper assessment ==="
+spctl --assess --type exec -v "$APP_PATH" || echo "Note: Gatekeeper may reject until notarized"
+
+echo "Code signing complete: $APP_PATH"