Add Chrome for Testing support for reliable WebDriver automation

- Add setup script (scripts/setup-chrome-for-testing.sh) that downloads
  matching Chrome and ChromeDriver versions from Google's CDN
- Add chrome_binary config option to specify custom Chrome binary path
- Update ChromeDriver to support custom binary via with_port_headless_and_binary()
- Update README with Chrome for Testing setup instructions
- Update config.example.toml with chrome_binary documentation

Chrome for Testing is Google's dedicated browser for automated testing
that guarantees version compatibility with ChromeDriver, avoiding the
common 'version mismatch' errors when Chrome auto-updates.

scripts/setup-chrome-for-testing.sh

@@ -0,0 +1,116 @@
+#!/bin/bash
+# Setup Chrome for Testing with matching ChromeDriver
+# This ensures version compatibility for WebDriver automation
+
+set -e
+
+# Configuration
+INSTALL_DIR="${HOME}/.chrome-for-testing"
+BIN_DIR="${HOME}/.local/bin"
+
+# Detect architecture
+ARCH=$(uname -m)
+if [ "$ARCH" = "arm64" ]; then
+    PLATFORM="mac-arm64"
+elif [ "$ARCH" = "x86_64" ]; then
+    PLATFORM="mac-x64"
+else
+    echo "❌ Unsupported architecture: $ARCH"
+    exit 1
+fi
+
+echo "🔍 Detecting platform: $PLATFORM"
+
+# Get latest stable version info
+echo "📡 Fetching latest Chrome for Testing version..."
+VERSION_JSON=$(curl -s 'https://googlechromelabs.github.io/chrome-for-testing/last-known-good-versions-with-downloads.json')
+VERSION=$(echo "$VERSION_JSON" | python3 -c "import json,sys; print(json.load(sys.stdin)['channels']['Stable']['version'])")
+
+echo "📦 Latest stable version: $VERSION"
+
+# Get download URLs
+CHROME_URL=$(echo "$VERSION_JSON" | python3 -c "
+import json,sys
+data = json.load(sys.stdin)
+for d in data['channels']['Stable']['downloads']['chrome']:
+    if d['platform'] == '$PLATFORM':
+        print(d['url'])
+        break
+")
+
+CHROMEDRIVER_URL=$(echo "$VERSION_JSON" | python3 -c "
+import json,sys
+data = json.load(sys.stdin)
+for d in data['channels']['Stable']['downloads']['chromedriver']:
+    if d['platform'] == '$PLATFORM':
+        print(d['url'])
+        break
+")
+
+# Create directories
+mkdir -p "$INSTALL_DIR"
+mkdir -p "$BIN_DIR"
+
+# Download and extract Chrome for Testing
+echo "⬇️  Downloading Chrome for Testing..."
+cd "$INSTALL_DIR"
+curl -L -o chrome.zip "$CHROME_URL"
+unzip -q -o chrome.zip
+rm chrome.zip
+
+# The extracted folder name varies by platform
+CHROME_APP_DIR="chrome-$PLATFORM"
+if [ -d "$CHROME_APP_DIR" ]; then
+    echo "✅ Chrome for Testing installed to: $INSTALL_DIR/$CHROME_APP_DIR"
+else
+    echo "❌ Chrome extraction failed"
+    exit 1
+fi
+
+# Download and extract ChromeDriver
+echo "⬇️  Downloading ChromeDriver..."
+curl -L -o chromedriver.zip "$CHROMEDRIVER_URL"
+unzip -q -o chromedriver.zip
+rm chromedriver.zip
+
+CHROMEDRIVER_DIR="chromedriver-$PLATFORM"
+if [ -f "$CHROMEDRIVER_DIR/chromedriver" ]; then
+    # Create symlink in bin directory
+    ln -sf "$INSTALL_DIR/$CHROMEDRIVER_DIR/chromedriver" "$BIN_DIR/chromedriver-for-testing"
+    chmod +x "$INSTALL_DIR/$CHROMEDRIVER_DIR/chromedriver"
+    echo "✅ ChromeDriver installed and linked to: $BIN_DIR/chromedriver-for-testing"
+else
+    echo "❌ ChromeDriver extraction failed"
+    exit 1
+fi
+
+# Create a wrapper script that uses Chrome for Testing
+cat > "$BIN_DIR/chrome-for-testing" << 'EOF'
+#!/bin/bash
+INSTALL_DIR="${HOME}/.chrome-for-testing"
+ARCH=$(uname -m)
+if [ "$ARCH" = "arm64" ]; then
+    PLATFORM="mac-arm64"
+else
+    PLATFORM="mac-x64"
+fi
+exec "$INSTALL_DIR/chrome-$PLATFORM/Google Chrome for Testing.app/Contents/MacOS/Google Chrome for Testing" "$@"
+EOF
+chmod +x "$BIN_DIR/chrome-for-testing"
+
+echo ""
+echo "✅ Setup complete!"
+echo ""
+echo "Installed versions:"
+echo "  Chrome for Testing: $VERSION"
+echo "  ChromeDriver: $VERSION"
+echo ""
+echo "Binaries:"
+echo "  Chrome: $BIN_DIR/chrome-for-testing"
+echo "  ChromeDriver: $BIN_DIR/chromedriver-for-testing"
+echo ""
+echo "To use with g3, make sure $BIN_DIR is in your PATH:"
+echo "  export PATH=\"$BIN_DIR:\$PATH\""
+echo ""
+echo "Or add to your shell profile (~/.zshrc or ~/.bashrc):"
+echo "  echo 'export PATH=\"$BIN_DIR:\$PATH\"' >> ~/.zshrc"