fix(utils): coerce Tavily usage counters to int

JSON APIs sometimes return numeric fields as strings; subtracting them raised TypeError and /status dropped the usage block.

nanobot/utils/searchusage.py

@@ -146,8 +146,8 @@ def _parse_tavily_usage(data: dict[str, Any]) -> SearchUsageInfo:
     }
     """
     account = data.get("account") or {}
-    used = account.get("plan_usage")
-    limit = account.get("plan_limit")
+    used = _optional_int(account.get("plan_usage"))
+    limit = _optional_int(account.get("plan_limit"))
 
     # Compute remaining
     remaining = None
@@ -160,9 +160,19 @@ def _parse_tavily_usage(data: dict[str, Any]) -> SearchUsageInfo:
         used=used,
         limit=limit,
         remaining=remaining,
-        search_used=account.get("search_usage"),
-        extract_used=account.get("extract_usage"),
-        crawl_used=account.get("crawl_usage"),
+        search_used=_optional_int(account.get("search_usage")),
+        extract_used=_optional_int(account.get("extract_usage")),
+        crawl_used=_optional_int(account.get("crawl_usage")),
     )
 
 
+def _optional_int(value: Any) -> int | None:
+    """Coerce JSON numerics (including string forms) to int; else None."""
+    if value is None:
+        return None
+    try:
+        return int(value)
+    except (TypeError, ValueError):
+        return None
+
+