feat(infra): Phase 2 monitoring agent — rule-first + 시놀로지 Chat 알림

5분 cron용 agent. docker/disk/health/network 4개 체크.
asyncssh 로그 억제, 작은 파티션(< 1G) 무시.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infra/core/system.py

@@ -27,6 +27,10 @@ def _parse_df(output: str) -> list[FileSystemInfo]:
             continue
         if parts[0] in ("tmpfs", "devtmpfs", "overlay", "shm", "none"):
             continue
+        # Skip tiny partitions (< 1G) — boot/system/snap, not worth monitoring
+        total_str = parts[1]
+        if total_str.endswith(("K", "Ki", "M", "Mi")) and not total_str.endswith(("G", "Gi", "T", "Ti")):
+            continue
 
         try:
             used_pct = int(parts[4].rstrip("%"))