Fix save on Docker bind-mount: write in-place instead of atomic rename

os.replace (rename) changes the inode which Docker bind-mounts prohibit
(EBUSY). Write directly to the file instead; a single-process writer
with RLock is safe without atomic rename.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/settings/config.py

@@ -1,6 +1,4 @@
 import json
-import os
-import tempfile
 import threading
 from typing import Optional
 
@@ -120,13 +118,5 @@ class Config():
 
     def __save(self) -> None:
         with self.__lock:
-            directory = os.path.dirname(os.path.abspath(self.__filename))
-            fd, tmp_path = tempfile.mkstemp(dir=directory, suffix='.tmp')
-            try:
-                with os.fdopen(fd, 'w') as f:
-                    json.dump(self.__config, f, ensure_ascii=False, indent=4)
-                os.replace(tmp_path, self.__filename)
-            except Exception:
-                if os.path.exists(tmp_path):
-                    os.remove(tmp_path)
-                raise
+            with open(self.__filename, 'w', encoding='utf-8') as f:
+                json.dump(self.__config, f, ensure_ascii=False, indent=4)