Fix/geohash blocks (#483)

* fix(geo-block): enable block/unblock for geohash users and enforce blocks\n\n- Add persisted set of blocked Nostr pubkeys in SecureIdentityStateManager\n- Check Nostr blocks for incoming messages (public + geo DMs)\n- Prevent sending geo DMs to blocked users\n- Extend /block and /unblock to resolve geohash display names to pubkeys and act accordingly\n- Improve /block list to show geohash blocks (visible names or #suffix)

* fix(geo-block): enforce blocks on geohash public and DM receive; add block/unblock actions to geohash people list

* fix: mark handlePublicMessage as @MainActor to call isMessageBlocked safely

* ui(block): show blocked indicator (nosign icon) next to blocked peers in mesh and geohash lists

* fix(geo-block): early-drop blocked pubkeys on geohash receive; filter blocked users from participants list

* fix(geo-block): purge existing geohash messages/DMs on block; block directly from chat using Nostr sender ID when available

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Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Views/MeshPeerList.swift

@@ -75,6 +75,14 @@ struct MeshPeerList: View {
                             }
                         }
 
+                        // Blocked indicator
+                        if !isMe, viewModel.isPeerBlocked(peer.id) {
+                            Image(systemName: "nosign")
+                                .font(.system(size: 10))
+                                .foregroundColor(.red)
+                                .help("Blocked")
+                        }
+
                         if let icon = item.enc.icon, !isMe {
                             Image(systemName: icon)
                                 .font(.system(size: 10))