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/api/rpc/federation/handlers.rs

@@ -364,7 +364,20 @@ impl RpcHandler {
         }
 
         let nodes = federation::load_nodes(&self.config.data_dir).await?;
-        if nodes.iter().any(|n| n.did == did) {
+        if let Some(existing) = nodes.iter().find(|n| n.did == did) {
+            // If already known but missing onion/pubkey, update them
+            if existing.onion.is_empty() || existing.pubkey.is_empty() {
+                let mut updated = existing.clone();
+                if existing.onion.is_empty() && !onion.is_empty() {
+                    updated.onion = onion.to_string();
+                }
+                if existing.pubkey.is_empty() && !pubkey.is_empty() {
+                    updated.pubkey = pubkey.to_string();
+                }
+                updated.last_seen = Some(chrono::Utc::now().to_rfc3339());
+                federation::update_node(&self.config.data_dir, &updated).await?;
+                info!(peer_did = %did, peer_onion = %onion, "Updated existing peer with missing onion/pubkey");
+            }
             return Ok(serde_json::json!({ "accepted": true, "already_known": true }));
         }