Add auto memory distillation scheduler (APScheduler)

- scheduler.py: AsyncIOScheduler with three cron jobs
    short  daily     03:00 (no LLM, always fast)
    mid    weekly    Sun 03:30 (LLM)
    long   monthly   1st 04:00 (LLM — off by default)
- config.py: AUTO_DISTILL, AUTO_DISTILL_SHORT/MID/LONG .env flags
- main.py: start/stop scheduler in FastAPI lifespan
- routers/distill.py: GET /distill/status — next run times + config
- requirements.txt: apscheduler>=3.10
- HELP.md: updated planned items, added /distill/status to API table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/routers/distill.py

@@ -8,10 +8,26 @@ Manual memory distillation endpoints.
 """
 from fastapi import APIRouter
 from memory_distiller import distill_short, distill_mid, distill_long
+import scheduler
 
 router = APIRouter(prefix="/distill")
 
 
+@router.get("/status")
+async def distill_status() -> dict:
+    """Show auto-distillation schedule and next run times."""
+    from config import settings
+    return {
+        "enabled": settings.auto_distill,
+        "jobs": scheduler.status(),
+        "config": {
+            "short": settings.auto_distill_short,
+            "mid": settings.auto_distill_mid,
+            "long": settings.auto_distill_long,
+        },
+    }
+
+
 @router.post("/short")
 async def do_distill_short() -> dict:
     return {"ok": True, **distill_short()}