refactor(backend): alihkan Settings ke zesdex-cms JsonSettingsRepository

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/zesdex-backend/src/model/mod.rs

@@ -2,9 +2,6 @@
 //! plus local sub-modules (agent_def, msglog) that weren't extracted.
 
 // Module re-exports matching original `crate::model::*` paths
-pub mod settings {
-    pub use zesdex_entities::seaorm::common::settings::*;
-}
 pub mod app_config {
     pub use zesdex_entities::seaorm::common::app_config::*;
 }