refactor(manager-core): share resolve_app helper across handlers

apps_api.rs and app_members_api.rs each grew a near-identical local
`resolve_app` that parses an id-or-slug param and translates None into
their own AppNotFound variant. Promote the lookup half to
`app_repo::resolve_app` (returns `Result<Option<AppLookup>, ...>`) and
let callers handle the None → not-found mapping.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/src/apps_api.rs

@@ -454,16 +454,7 @@ async fn resolve_app(
     apps: &dyn AppRepository,
     ident: &str,
 ) -> Result<crate::app_repo::AppLookup, AppsApiError> {
-    if let Ok(uuid) = ident.parse::<Uuid>() {
-        if let Some(app) = apps.get_by_id(AppId::from(uuid)).await? {
-            return Ok(crate::app_repo::AppLookup {
-                app,
-                redirected: false,
-            });
-        }
-        return Err(AppsApiError::AppNotFound(ident.to_string()));
-    }
-    apps.get_by_slug_or_history(ident)
+    crate::app_repo::resolve_app(apps, ident)
         .await?
         .ok_or_else(|| AppsApiError::AppNotFound(ident.to_string()))
 }