fix(federation,cloud): dedup trusted nodes + chat contacts by onion; guard cloud my-folders (B1,B2,B4)

B1/B2: the same physical node can linger in the federation list under two
dids (e.g. after a did/key change). An onion is a node's unique stable
identity, so two entries with the same onion are one node. This showed the
node twice in the trusted-node list (B1) and as two mesh chat contacts —
one by name+logo, one by raw did (B2).
- storage::load_nodes now collapses same-onion entries (keep first, merge
  fips_npub/name/last_state) so every consumer (list + chat seed + sync)
  sees one entry per node.
- federation::sync merge_transitive_peers also matches by onion (not just
  did) so new transitive hints don't re-add a known node under a new did.
- mesh::seed_federation_peers_into_mesh skips already-seeded onions (belt
  and suspenders).
- Unit tests for dedup_nodes_by_onion (collapse + onion-suffix handling).

B4: filebrowser-client.listDirectory only checked res.ok before res.json(),
so when File Browser is absent (nginx serves the SPA index.html, 200) or
down (502) the JSON parse threw the opaque "Unexpected token '<'". Now it
checks the content-type and throws a friendly "File Browser is not
available" the Cloud view already renders as an empty state.

Verified: dedup unit tests 2/2; live .198 (15 entries→13 distinct onions)
restarted healthy on new binary; B4 guard present in built bundle + deployed.

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

core/archipelago/src/federation/sync.rs

@@ -145,6 +145,27 @@ async fn merge_transitive_peers(
             }
             continue;
         }
+        // Same physical node advertised under a DIFFERENT did? Match on the
+        // onion (its stable network identity). Without this, a node that
+        // appears under two dids (e.g. after a key/did change) gets added
+        // twice — showing up duplicated in the trusted-node list (B1) and as
+        // two separate mesh chat contacts (B2). Merge into the existing entry.
+        let hint_onion = hint.onion.trim_end_matches(".onion");
+        if !hint_onion.is_empty() {
+            if let Some(existing) = nodes
+                .iter_mut()
+                .find(|n| n.onion.trim_end_matches(".onion") == hint_onion)
+            {
+                if existing.fips_npub.is_none() && hint.fips_npub.is_some() {
+                    existing.fips_npub = hint.fips_npub.clone();
+                }
+                if existing.name.is_none() && hint.name.is_some() {
+                    existing.name = hint.name.clone();
+                }
+                refreshed += 1;
+                continue;
+            }
+        }
         nodes.push(FederatedNode {
             did: hint.did.clone(),
             pubkey: hint.pubkey.clone(),