Audit fixes: LIVE symbols/fills/expiry/pending, security harden, add 更新说明.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/env_store.py

@@ -22,14 +22,12 @@ def upsert_env_keys(updates: dict[str, str]) -> Path | None:
     return target
 
 
-def mask_secret(raw: str | None, *, keep: int = 4) -> str | None:
-    """脱敏：****末尾；过短则全部打码。"""
+def mask_secret(raw: str | None, *, keep: int = 0) -> str | None:
+    """脱敏：仅返回是否已配置（不再泄露末尾字符）。"""
     s = (raw or "").strip()
     if not s:
         return None
-    if len(s) <= keep:
-        return "*" * len(s)
-    return "*" * max(4, len(s) - keep) + s[-keep:]
+    return "********"
 
 
 def okx_keys_configured(s=None) -> bool: