fix(log): remove noisy no-op logs from auto-compact

Remove two debug log lines that fire on every idle channel check:
- "scheduling archival" (logged before knowing if there's work)
- "skipping, no un-consolidated messages" (the common no-op path)

The meaningful "archived" info log (only on real work) is preserved.

nanobot/agent/autocompact.py

@@ -70,7 +70,6 @@ class AutoCompact:
                 continue
             if self._is_expired(info.get("updated_at"), now):
                 self._archiving.add(key)
-                logger.debug("Auto-compact: scheduling archival for {} (idle > {} min)", key, self._ttl)
                 schedule_background(self._archive(key))
 
     async def _archive(self, key: str) -> None:
@@ -79,7 +78,6 @@ class AutoCompact:
             session = self.sessions.get_or_create(key)
             archive_msgs, kept_msgs = self._split_unconsolidated(session)
             if not archive_msgs and not kept_msgs:
-                logger.debug("Auto-compact: skipping {}, no un-consolidated messages", key)
                 session.updated_at = datetime.now()
                 self.sessions.save(session)
                 return
@@ -95,13 +93,14 @@ class AutoCompact:
             session.last_consolidated = 0
             session.updated_at = datetime.now()
             self.sessions.save(session)
-            logger.info(
-                "Auto-compact: archived {} (archived={}, kept={}, summary={})",
-                key,
-                len(archive_msgs),
-                len(kept_msgs),
-                bool(summary),
-            )
+            if archive_msgs:
+                logger.info(
+                    "Auto-compact: archived {} (archived={}, kept={}, summary={})",
+                    key,
+                    len(archive_msgs),
+                    len(kept_msgs),
+                    bool(summary),
+                )
         except Exception:
             logger.exception("Auto-compact: failed for {}", key)
         finally: