fix(api): model Opus pakai URL + API custom dari ~/.claude/settings.json

Perbaiki provider claude agar selalu refresh dari settings.json dan
menjadi default (claude-opus-4-8) setiap startup:

- fix(app_config_repo): ganti or_insert -> insert untuk provider claude —
  base_url/key dari ~/.claude/settings.json selalu di-refresh, tidak
  tertutup snapshot lama app_config.json.
- fix(app_config_repo): hapus kondisi default_provider == default — saat
  settings.json terdeteksi, default_provider='claude' dan
  default_model='claude-opus-4-8' SELALU di-set (sebelumnya skip kalau
  user pernah ganti provider).
- fix(subagent/provider): resolve_subagent_provider fallback ke
  app_config.default_provider/default_model kalau settings.provider/model
  kosong — subagent ikut pakai Opus.
- test: 4 unit test (parse settings.json, refresh stale provider, custom
  model, env fallback). Verified live: settings.json terbaca (9router URL
  + key).

apps/infrastructure/src/subagent/provider.rs

@@ -63,15 +63,21 @@ impl SubagentProvider {
 
 /// Resolve subagent provider and model from settings.
 ///
-/// Flow: reads `settings.provider` and `settings.model` → if model is empty,
+/// Flow: reads `settings.provider` and `settings.model` → if provider is
+/// empty, falls back to `app_config.default_provider` → if model is empty,
 /// falls back to the provider config's `default_model` → if that is also
-/// empty, uses the domain default model constant.
+/// empty, uses `app_config.default_model` → finally the domain default model
+/// constant.
 #[instrument]
 pub fn resolve_subagent_provider(
     settings: &zesdex_domain::cms::Settings,
     app_config: &zesdex_domain::cms::AppConfig,
 ) -> (String, String) {
-    let provider = settings.provider.clone();
+    let provider = if settings.provider.is_empty() {
+        app_config.default_provider.clone()
+    } else {
+        settings.provider.clone()
+    };
     let model = settings.model.clone();
 
     // Use the default model from the provider config if available
@@ -80,6 +86,7 @@ pub fn resolve_subagent_provider(
             .providers
             .get(&provider)
             .and_then(|p| p.default_model.clone())
+            .or_else(|| Some(app_config.default_model.clone()))
             .unwrap_or_else(|| zesdex_domain::agent::defaults::DEFAULT_MODEL.to_string())
     } else {
         model