fix: settings PUT 后热更新内存 — 无需重启即生效

问题：修改 Telegram 等设置后需要重启服务器才能生效，
因为 load_settings_from_db() 只在启动时运行。

修复：PUT /api/settings/{key} 写入 DB 后，
同步更新 settings 内存对象（DB_OVERRIDE_MAP 映射 + INT_SETTINGS 类型转换）。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/api/settings.py

@@ -102,13 +102,29 @@ async def set_setting(
     admin: Admin = Depends(get_current_admin),
     db: AsyncSession = Depends(get_db),
 ):
-    """Set a system setting value (immutable keys are rejected)"""
+    """Set a system setting value (immutable keys are rejected)
+
+    Writes to DB AND hot-reloads the in-memory settings object so changes
+    take effect immediately without server restart.
+    """
     if key in IMMUTABLE_KEYS:
         raise HTTPException(status_code=403, detail=f"Setting '{key}' is immutable and cannot be modified via API")
 
     repo = SettingRepositoryImpl(db)
     setting = await repo.set(key, str(payload.value))
 
+    # Hot-reload: update in-memory settings so changes take effect immediately
+    from server.config import settings as _settings
+    attr_name = _settings.DB_OVERRIDE_MAP.get(key)
+    if attr_name and hasattr(_settings, attr_name):
+        value = setting.value
+        if attr_name in _settings.INT_SETTINGS:
+            try:
+                value = int(value)
+            except (ValueError, TypeError):
+                pass
+        setattr(_settings, attr_name, value)
+
     # Audit log
     audit_repo = AuditLogRepositoryImpl(db)
     await audit_repo.create(AuditLog(