feat(suppress): group-suppress warnings + ls + journey + docs (M1.5)

- dangling_suppress_warnings takes an ApplyOwner and walks the group's own
  chain (GROUP_CHAIN_LEVELS_CTE) for a group node; runs for both owners.
- GET /groups/{id}/suppressions + `pic suppress ls --group` (client + cmd +
  main.rs; --app/--group mutually exclusive).
- suppress journey: a child group declines a parent template for its subtree;
  suppress ls --group shows the marker. Docs §4.5 + CLAUDE.md move group-level
  suppression from Deferred to implemented.

Completes M1. (An unrelated pre-existing email_inbound dispatch-timing flake
passes in isolation.)

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

crates/manager-core/src/apply_api.rs

@@ -45,6 +45,7 @@ pub fn apply_router(service: ApplyService) -> Router {
         .route("/groups/{id}/triggers", get(group_triggers_handler))
         .route("/groups/{id}/routes", get(group_routes_handler))
         .route("/apps/{id}/suppressions", get(app_suppressions_handler))
+        .route("/groups/{id}/suppressions", get(group_suppressions_handler))
         .with_state(service)
 }
 
@@ -64,6 +65,26 @@ async fn app_suppressions_handler(
     Ok(Json(report))
 }
 
+/// Read-only §11 tail M1 suppression report for a group: the inherited templates
+/// it declines for its whole subtree (`target_kind`, `reference`). Viewer-tier
+/// `GroupScriptsRead`. Backs `pic suppress ls --group`.
+async fn group_suppressions_handler(
+    State(svc): State<ApplyService>,
+    Extension(principal): Extension<Principal>,
+    Path(id_or_slug): Path<String>,
+) -> Result<Json<Vec<SuppressionInfo>>, ApplyError> {
+    let group_id = resolve_group_id(svc.groups.as_ref(), &id_or_slug).await?;
+    require(
+        svc.authz.as_ref(),
+        &principal,
+        Capability::GroupScriptsRead(group_id),
+    )
+    .await
+    .map_err(map_authz)?;
+    let report = svc.suppression_report(ApplyOwner::Group(group_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`.