feat: add proactive cron tasks and systemd timers\n\n- 10 proactive tasks: ingest with self-healing & link suggestions, daily summary, health check, archive stale, tag normalizer, predictive links, auto assign review, import context buffer\n- systemd timers for scheduling (02:00/14:00 slots, 30min intervals, weekly)\n- all tasks tested and working\n\nRefs: #1

systemd/openclaw-secondbrain-import-context-buffer.timer

@@ -0,0 +1,10 @@
+[Unit]
+Description=Import Context Buffer every 4 hours
+PartOf=openclaw-secondbrain.target
+
+[Timer]
+OnCalendar=*-*-* 02,06,10,14,18,22:00:00
+Persistent=true
+
+[Install]
+WantedBy=timers.target