fix(auth): preserve corrupt auth.json and warn instead of silently resetting

_load_auth_store() caught all parse/read exceptions and silently
returned an empty store, making corruption look like a logout with
no diagnostic information and no way to recover the original file.

Now copies the corrupt file to auth.json.corrupt before resetting,
and logs a warning with the exception and backup path.

hermes_cli/auth.py

@@ -743,7 +743,18 @@ def _load_auth_store(auth_file: Optional[Path] = None) -> Dict[str, Any]:
 
     try:
         raw = json.loads(auth_file.read_text())
+    except Exception as exc:
+        corrupt_path = auth_file.with_suffix(".json.corrupt")
+        try:
+            import shutil
+            shutil.copy2(auth_file, corrupt_path)
         except Exception:
+            pass
+        logger.warning(
+            "auth: failed to parse %s (%s) — starting with empty store. "
+            "Corrupt file preserved at %s",
+            auth_file, exc, corrupt_path,
+        )
         return {"version": AUTH_STORE_VERSION, "providers": {}}
 
     if isinstance(raw, dict) and (