feat(suppress): pic suppress ls --app + dangling-suppress warning (§11 tail S4)

Visibility + typo guard.

- `pic suppress ls --app <a>` — read-only (kind, reference):
  ApplyService::suppression_report(App) → GET /apps/{id}/suppressions
  (viewer-tier AppRead), client + cmd + main.rs wiring.
- Dangling-suppress warning: at apply, a suppress reference that matches no
  inherited template on the app's chain (no ancestor-group trigger bound to
  that script name / no ancestor-group route at that path) emits an
  ApplyReport warning — the suppression silently does nothing otherwise.
  Soft (never fails the apply), reusing the existing warnings channel.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/src/apply_api.rs

@@ -18,8 +18,8 @@ use serde_json::json;
 use crate::app_repo::AppRepository;
 use crate::apply_service::{
     ApplyError, ApplyOwner, ApplyReport, ApplyService, Bundle, BundleTrigger, CollectionInfo,
-    ExtensionPointInfo, NodeKind, PlanResult, RouteTemplateInfo, TreeBundle, TreePlanResult,
-    TriggerTemplateInfo,
+    ExtensionPointInfo, NodeKind, PlanResult, RouteTemplateInfo, SuppressionInfo, TreeBundle,
+    TreePlanResult, TriggerTemplateInfo,
 };
 use crate::authz::{require, AuthzDenied, Capability};
 use crate::group_repo::GroupRepository;
@@ -44,9 +44,26 @@ pub fn apply_router(service: ApplyService) -> Router {
         .route("/groups/{id}/collections", get(group_collections_handler))
         .route("/groups/{id}/triggers", get(group_triggers_handler))
         .route("/groups/{id}/routes", get(group_routes_handler))
+        .route("/apps/{id}/suppressions", get(app_suppressions_handler))
         .with_state(service)
 }
 
+/// Read-only §11 tail suppression report for an app: the inherited templates it
+/// declines (`target_kind`, `reference`). Viewer-tier `AppRead`. Backs
+/// `pic suppress ls --app`.
+async fn app_suppressions_handler(
+    State(svc): State<ApplyService>,
+    Extension(principal): Extension<Principal>,
+    Path(id_or_slug): Path<String>,
+) -> Result<Json<Vec<SuppressionInfo>>, ApplyError> {
+    let app_id = resolve_app_id(svc.apps.as_ref(), &id_or_slug).await?;
+    require(svc.authz.as_ref(), &principal, Capability::AppRead(app_id))
+        .await
+        .map_err(map_authz)?;
+    let report = svc.suppression_report(ApplyOwner::App(app_id)).await?;
+    Ok(Json(report))
+}
+
 /// Read-only §11 tail route-template report for a group: its own declared route
 /// templates (method, host, path, handler script, dispatch, enabled). Viewer-
 /// tier read. Backs `pic routes ls --group`.