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.

crates/g3-computer-control/src/webdriver/chrome.rs

@@ -19,8 +19,18 @@ impl ChromeDriver {
         Self::with_port_headless(9515).await
     }
 
+    /// Create a new ChromeDriver instance with Chrome for Testing binary
+    pub async fn new_headless_with_binary(chrome_binary: &str) -> Result<Self> {
+        Self::with_port_headless_and_binary(9515, Some(chrome_binary)).await
+    }
+
     /// Create a new ChromeDriver instance with a custom port in headless mode
     pub async fn with_port_headless(port: u16) -> Result<Self> {
+        Self::with_port_headless_and_binary(port, None).await
+    }
+
+    /// Create a new ChromeDriver instance with a custom port and optional Chrome binary path
+    pub async fn with_port_headless_and_binary(port: u16, chrome_binary: Option<&str>) -> Result<Self> {
         let url = format!("http://localhost:{}", port);
 
         let mut caps = serde_json::Map::new();
@@ -41,6 +51,12 @@ impl ChromeDriver {
                 Value::String("--window-size=1920,1080".to_string()),
             ]),
         );
+
+        // If a custom Chrome binary is specified, use it
+        if let Some(binary) = chrome_binary {
+            chrome_options.insert("binary".to_string(), Value::String(binary.to_string()));
+        }
+
         caps.insert(
             "goog:chromeOptions".to_string(),
             Value::Object(chrome_options),

crates/g3-config/src/lib.rs

@@ -132,6 +132,10 @@ pub struct WebDriverConfig {
     #[serde(default)]
     pub chrome_port: u16,
     #[serde(default)]
+    /// Optional path to Chrome binary (e.g., Chrome for Testing)
+    /// If not set, ChromeDriver will use the default Chrome installation
+    pub chrome_binary: Option<String>,
+    #[serde(default)]
     pub browser: WebDriverBrowser,
 }
 
@@ -152,6 +156,7 @@ impl Default for WebDriverConfig {
             enabled: true,
             safari_port: 4444,
             chrome_port: 9515,
+            chrome_binary: None,
             browser: WebDriverBrowser::ChromeHeadless,
         }
     }

crates/g3-core/src/lib.rs

@@ -5605,8 +5605,13 @@ impl<W: UiWriter> Agent<W> {
                             // Wait before each attempt (200ms between retries, total max ~2s)
                             tokio::time::sleep(tokio::time::Duration::from_millis(200)).await;
                             
-                            // Try to connect to ChromeDriver in headless mode
-                            match g3_computer_control::ChromeDriver::with_port_headless(port).await {
+                            // Try to connect to ChromeDriver in headless mode (with optional custom binary)
+                            let driver_result = match &self.config.webdriver.chrome_binary {
+                                Some(binary) => g3_computer_control::ChromeDriver::with_port_headless_and_binary(port, Some(binary)).await,
+                                None => g3_computer_control::ChromeDriver::with_port_headless(port).await,
+                            };
+                            
+                            match driver_result {
                                 Ok(driver) => {
                                     let session = std::sync::Arc::new(tokio::sync::Mutex::new(WebDriverSession::Chrome(driver)));
                                     *self.webdriver_session.write().await = Some(session);