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-console/examples/test_detector.rs

@@ -1,12 +1,12 @@
-use sysinfo::{System, Pid};
+use sysinfo::{Pid, System};
 
 fn main() {
     let mut sys = System::new_all();
     sys.refresh_processes();
-    
+
     // Test with known PIDs
     let pids = vec![68123, 72749];
-    
+
     for pid_num in pids {
         let pid = Pid::from_u32(pid_num);
         if let Some(process) = sys.process(pid) {