Add Chrome headless diagnostic tool

Runs automatically when --chrome-headless flag is used, checking:
- ChromeDriver installation and PATH
- Chrome/Chromium installation
- Chrome and ChromeDriver version compatibility
- config.toml chrome_binary setting
- Chrome for Testing installation
- ChromeDriver executable permissions (macOS quarantine)

Displays a detailed report with:
- Summary of detected versions and paths
- Pass/warning/error status for each check
- Specific fix suggestions for any issues found

Users can then ask g3 to help fix any detected issues.

crates/g3-computer-control/Cargo.toml

@@ -17,6 +17,7 @@ tracing = { workspace = true }
 uuid = { workspace = true }
 
 shellexpand = "3.1"
+dirs = "5.0"
 # Async trait support
 async-trait = "0.1"