fix(robustness): surface swallowed persistence-write failures + federation tombstone durability

§C of the 1.8.0 hardening plan: persistence writes whose Results were
silently dropped now log a warn/error with context (mesh contact
blocklist, scheduler state, content catalog, container registry,
update state, bitcoin relay, package install markers, server shutdown
state). §I: federation tombstones are now flushed durably in
storage/sync so cleared peers can't resurrect after a crash.

Tracker updated with shas in docs/1.8.0-RELEASE-HARDENING-PLAN.md.

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

core/archipelago/src/container/registry.rs

@@ -155,7 +155,9 @@ pub async fn load_registries(data_dir: &Path) -> Result<RegistryConfig> {
                 .collect::<Vec<_>>();
     if changed {
         // Persist so the next load doesn't have to re-merge.
-        let _ = save_registries(data_dir, &config).await;
+        if let Err(e) = save_registries(data_dir, &config).await {
+            tracing::warn!("Failed to persist migrated registry config: {e:#}");
+        }
     }
     Ok(config)
 }