fix(fips,federation,ui): mesh content browse, removed-node tombstones, modal sizing

FIPS peer content browse over the mesh was failing with "Peer returned
error: 404 Not Found" and never falling back to Tor. `is_peer_allowed_path`
only allowed `/content/<id>` (item fetches) — the catalog endpoint is
exactly `/content` (no trailing slash), so it 404'd over the FIPS peer
listener. A FIPS 404 was also treated as a successful response, so the dial
never retried Tor. Fixes: allow `/content` over the mesh; add
`fips_should_fall_back()` so a FIPS 404/5xx in Auto mode falls back to Tor
(handles version-skew peers reaching a different route). Also correct the
reconnect hint text — the public anchor is TCP/8443, not UDP/8668.

Federation: deleted nodes reappeared because transitive discovery
(`merge` of a peer's advertised trusted peers) re-added any unknown DID.
Add a tombstone store (`removed-nodes.json`): remove_node tombstones the
DID, transitive merge skips tombstoned DIDs, and a remote-triggered
peer-joined is ignored for a removed DID. Explicit local re-add (add_node)
clears the tombstone.

UI: the app credentials modal panel stretched edge-to-edge (height:100%,
max-width:none, items-stretch overlay). Constrain it to a centered card
(max-width 34rem, rounded, dimmed full-screen backdrop) matching the
AppIconGrid / wallet-receive modal.

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

core/archipelago/src/federation/sync.rs

@@ -118,6 +118,12 @@ async fn merge_transitive_peers(
         return Ok(());
     }
     let mut nodes = super::storage::load_nodes(data_dir).await?;
+    // Tombstoned DIDs: peers the operator explicitly removed. Never re-add
+    // them via transitive discovery, or deleted (e.g. stale test) nodes
+    // reappear on the next sync with any peer that still lists them.
+    let removed = super::storage::load_removed_dids(data_dir)
+        .await
+        .unwrap_or_default();
     let mut added = 0u32;
     let mut refreshed = 0u32;
 
@@ -127,6 +133,10 @@ async fn merge_transitive_peers(
         if hint.did == source_did || hint.did == local_did {
             continue;
         }
+        // Skip anything the operator deliberately removed.
+        if removed.contains(&hint.did) {
+            continue;
+        }
         if let Some(existing) = nodes.iter_mut().find(|n| n.did == hint.did) {
             // Already known — just refresh fips_npub if we didn't have one.
             if existing.fips_npub.is_none() && hint.fips_npub.is_some() {