refactor(backend): alihkan AppConfig ke zesdex-cms JsonAppConfigRepository

Semua pemanggilan AppConfig::load() diganti dengan
JsonAppConfigRepository + AppConfigRepository trait.
Re-export model::app_config dihapus dari model/mod.rs.

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

crates/zesdex-backend/src/app/subagent/engine.rs

@@ -15,6 +15,7 @@ use crate::dto::provider::request::ToolDef;
 use crate::tool::{all_tools, tool_defs, tool_is_risky};
 use super::context::SubagentContext;
 use super::event::SubagentEvent;
+use zesdex_cms::domain::repository::AppConfigRepository;
 use zesdex_cms::domain::repository::SettingsRepository;
 
 /// Maps a subagent's allowed tool names to concrete Tool trait objects and
@@ -63,7 +64,9 @@ fn resolve_provider_config() -> (String, String, Option<String>, String) {
     let settings = zesdex_cms::infrastructure::persistence::settings_repo::JsonSettingsRepository::new()
         .load(&store_base_dir)
         .unwrap_or_default();
-    let app_config = crate::model::app_config::AppConfig::load();
+    let app_config = zesdex_cms::infrastructure::persistence::app_config_repo::JsonAppConfigRepository::new()
+        .load(&store_base_dir)
+        .unwrap_or_default();
 
     let mut api_key = settings.api_keys.get(&settings.provider).cloned().unwrap_or_else(|| {
         tracing::warn!("[subagent] no API key for provider '{}' in settings, trying env/default", settings.provider);