fix(reconciler): recreate an absent stack member when its siblings are live

The periodic reconcile runs ExistingOnly — merely listing a catalog
manifest must never install an app — and its only absent-container
recovery keyed on the last running-names snapshot, which ages out after
a few daemon restarts. An absent member of an installed stack then stays
absent forever: .38 ran indeedhub with no minio/postgres for days, nginx
down on 'host not found in upstream "minio"', and nothing ever put the
members back.

A live sibling container is proof the stack is installed on this node,
so an absent member is now treated as a hole to repair, not a choice to
respect: the recovery guard also fires when another member of the same
stack (app_ops::stack_member_app_ids) has a container in any state.
A stack with no containers at all is left untouched, and sibling app ids
resolve through the loaded-manifest container names (immich-postgres
runs as immich_postgres).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/app_ops.rs

@@ -75,7 +75,8 @@ pub fn address_caching_dependents(package_id: &str) -> &'static [&'static str] {
 /// The package whose lifecycle lock covers `app_id`: the stack package when
 /// `app_id` is a member (RPC ops on "mempool" hold the "mempool" lock while
 /// they drive archy-mempool-web), otherwise the app itself.
-fn owning_package(app_id: &str) -> &str {
+/// Also consulted by the reconciler's absent-stack-member recovery.
+pub fn owning_package(app_id: &str) -> &str {
     const STACKS: &[&str] = &[
         "immich",
         "indeedhub",