fix: federation peer-joined updates empty onion addresses

When a node was already known (via link-node) but had an empty onion
address, the peer-joined handler returned early without updating the
onion. Now it patches missing onion/pubkey fields on existing nodes.

Also adds update_node() to federation storage and updates the
architecture comparison doc with system resources, StartOS/umbrelOS
tabs, Web5 section, and comparison view.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/federation/storage.rs

@@ -96,6 +96,27 @@ pub async fn set_trust_level(
     Ok(nodes)
 }
 
+/// Update a federated node's metadata (onion, pubkey, name, last_seen).
+pub async fn update_node(data_dir: &Path, updated: &FederatedNode) -> Result<()> {
+    let mut nodes = load_nodes(data_dir).await?;
+    if let Some(node) = nodes.iter_mut().find(|n| n.did == updated.did) {
+        if !updated.onion.is_empty() {
+            node.onion = updated.onion.clone();
+        }
+        if !updated.pubkey.is_empty() {
+            node.pubkey = updated.pubkey.clone();
+        }
+        if updated.name.is_some() {
+            node.name = updated.name.clone();
+        }
+        if updated.last_seen.is_some() {
+            node.last_seen = updated.last_seen.clone();
+        }
+        save_nodes(data_dir, &nodes).await?;
+    }
+    Ok(())
+}
+
 pub async fn update_node_state(
     data_dir: &Path,
     did: &str,