Implement cleanup guard to prevent multiple executions on exit

- Introduced a new cleanup function that ensures terminal and browser sessions are cleaned up only once during application exit.
- Updated atexit registration to use the new cleanup function, enhancing resource management and preventing potential issues from multiple cleanup calls.
- Modified terminal cleanup messaging to only display when environments are cleaned, improving user feedback.

tools/terminal_tool.py

@@ -1406,7 +1406,8 @@ def cleanup_all_environments():
         except:
             pass
     
-    print(f"[Terminal Cleanup] Cleaned {cleaned} environments")
+    if not os.getenv("HERMES_QUIET") and cleaned > 0:
+        print(f"[Terminal Cleanup] Cleaned {cleaned} environments")
     return cleaned