feat: L4 session archiver + scheduler cron integration

- Add compress_session.py: compress raw model_responses into L4 archives
- Integrate 12h silent cron into scheduler.check() (runs before TASKS dir check)
- Whitelist compress_session.py in .gitignore (archives excluded)
- llmcore: refactor SSE warn handling, max_retries default 2->1
- scheduler: remove unused health_check(), INTERVAL 60->120

.gitignore

@@ -43,6 +43,11 @@ memory/*
 !memory/autonomous_operation_sop/**
 !memory/scheduled_task_sop.md
 
+# L4 session archiver (only the script, not archives)
+!memory/L4_raw_sessions/
+memory/L4_raw_sessions/*
+!memory/L4_raw_sessions/compress_session.py
+
 # ljqCtrl related tools
 !memory/ljqCtrl.py
 !memory/ljqCtrl_sop.md