add context window monitor

Writes the current context window to logs/current_context_window (uses a symlink to a session ID).

This PR was unfortunately generated by a different LLM and did a ton of superficial reformating, it's actually a fairly small and benign change, but I don't want to roll back everything. Hope that's ok.

crates/g3-computer-control/examples/test_screencapture_direct.rs

@@ -2,29 +2,33 @@ use std::process::Command;
 
 fn main() {
     let path = "/tmp/rust_screencapture_test.png";
-    
+
     println!("Testing screencapture command from Rust...");
-    
+
     let mut cmd = Command::new("screencapture");
     cmd.arg("-x"); // No sound
     cmd.arg(path);
-    
+
     println!("Command: {:?}", cmd);
-    
+
     match cmd.output() {
         Ok(output) => {
             println!("Exit status: {}", output.status);
             println!("Stdout: {}", String::from_utf8_lossy(&output.stdout));
             println!("Stderr: {}", String::from_utf8_lossy(&output.stderr));
-            
+
             if output.status.success() {
                 println!("\n✅ Screenshot saved to: {}", path);
-                
+
                 // Check file exists and size
                 if let Ok(metadata) = std::fs::metadata(path) {
-                    println!("File size: {} bytes ({:.1} MB)", metadata.len(), metadata.len() as f64 / 1_000_000.0);
+                    println!(
+                        "File size: {} bytes ({:.1} MB)",
+                        metadata.len(),
+                        metadata.len() as f64 / 1_000_000.0
+                    );
                 }
-                
+
                 // Open it
                 let _ = Command::new("open").arg(path).spawn();
                 println!("\nOpened screenshot - please verify it looks correct!");