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/src/lib.rs

@@ -1,5 +1,5 @@
 pub mod api;
+pub mod launch;
 pub mod logs;
 pub mod models;
 pub mod process;
-pub mod launch;