fix(admin-api): accept slug or UUID on per-app endpoints

The Queues tab at /admin/apps/default/queues was returning
"Cannot parse `app_id` with value `default`: UUID parsing failed".
27 admin endpoints across 6 files used strict `Path<AppId>` instead
of the canonical `Path<String>` + `resolve_app()` pattern from
app_repo.rs:34. Working endpoints (apps, app_members, users_admin)
all use the lenient pattern; this commit brings the remaining 6
files into line:

- queues_api.rs       — 2 handlers
- files_api.rs        — 2 handlers
- secrets_api.rs      — 3 handlers
- topics_api.rs       — 4 handlers
- dead_letters_api.rs — 5 handlers
- triggers_api.rs     — 10 handlers

The handler bodies (authz, repo calls) are unchanged; only the path
extractor and the per-file `ensure_app_exists` helper (now renamed
`resolve_app`) move. Lib tests updated to pass `.to_string()` at
the call site (Path now takes String, not AppId).

email_inbound_api.rs deliberately stays strict-UUID — it's a public
webhook receiver consumed by external providers, not by the
slug-based dashboard.

Adds Playwright spec `dashboard/tests/e2e/navigation/tabs.spec.ts`
covering every per-app tab (queues, files, dead-letters, users,
invitations, plus the main page hosting triggers/secrets/topics)
with a negative assertion against the "Cannot parse" error text
plus a focused regression test for the original queues report.

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

crates/manager-core/src/files_api.rs

@@ -76,10 +76,10 @@ struct ListFilesResponse {
 async fn list_files(
     State(s): State<FilesAdminState>,
     Extension(principal): Extension<Principal>,
-    Path(app_id): Path<AppId>,
+    Path(id_or_slug): Path<String>,
     Query(q): Query<ListFilesQuery>,
 ) -> Result<Json<ListFilesResponse>, FilesApiError> {
-    ensure_app_exists(&*s.apps, app_id).await?;
+    let app_id = resolve_app(&*s.apps, &id_or_slug).await?;
     require(
         s.authz.as_ref(),
         &principal,
@@ -123,9 +123,9 @@ async fn list_files(
 async fn delete_file(
     State(s): State<FilesAdminState>,
     Extension(principal): Extension<Principal>,
-    Path((app_id, collection, file_id)): Path<(AppId, String, String)>,
+    Path((id_or_slug, collection, file_id)): Path<(String, String, String)>,
 ) -> Result<StatusCode, FilesApiError> {
-    ensure_app_exists(&*s.apps, app_id).await?;
+    let app_id = resolve_app(&*s.apps, &id_or_slug).await?;
     require(
         s.authz.as_ref(),
         &principal,
@@ -139,12 +139,12 @@ async fn delete_file(
     Ok(StatusCode::NO_CONTENT)
 }
 
-async fn ensure_app_exists(apps: &dyn AppRepository, app_id: AppId) -> Result<(), FilesApiError> {
-    apps.get_by_id(app_id)
+async fn resolve_app(apps: &dyn AppRepository, ident: &str) -> Result<AppId, FilesApiError> {
+    crate::app_repo::resolve_app(apps, ident)
         .await
         .map_err(|e| FilesApiError::Backend(e.to_string()))?
-        .ok_or(FilesApiError::AppNotFound)?;
-    Ok(())
+        .map(|l| l.app.id)
+        .ok_or(FilesApiError::AppNotFound)
 }
 
 #[derive(Debug, thiserror::Error)]