Add mesh diagnostics: /ping, /trace, and topology map (#1377)

* Add mesh diagnostics: /ping, /trace, and topology map

- New protocol types ping=0x26 / pong=0x27 (9-byte payload: 8-byte nonce
  + origin TTL) with per-peer inbound rate limiting (5 per 10s)
- /ping @name reports RTT and hop count, 10s timeout
- /trace @name prints the estimated path from gossiped directNeighbors
- Topology map sheet (circular Canvas layout) reachable from App Info
- Ping/pong ride the deterministic directed-relay path like DMs
- Tests: payload round-trip, hop-count math, command output, edge
  normalization, layout

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Fix CI media-wipe race, per-link ping rate limiting, and /ping output routing

Three fixes for PR #1377 review:

1. CI flake (sendImage_privateChatProcessesAndTransfersImage): the
   panicClearAllData / clearCurrentPublicTimeline detached utility-priority
   tasks delete the real ~/Library/Application Support/files tree, which the
   test process shares. The wipe fires at a nondeterministic time and raced
   the sendImage test's JPEG in files/images/outgoing (write then re-read),
   so prepareImagePacket threw and the test timed out. Both wipes are now
   skipped under tests (existing TestEnvironment.isRunningTests pattern);
   this also stops test runs from deleting the developer's real media.

2. Codex P1: ping packets are unsigned, so keying the pong rate limiter on
   packet.senderID let one connected peer rotate forged sender IDs to bypass
   the 5-per-10s budget. The limiter now keys on the ingress link (the
   directly connected peer that delivered the packet); the pong still goes
   to the claimed sender. Regression test proves rotating senders over one
   link exhaust one budget (fails 10 vs 5 pongs on the old code).

3. Codex P2: /ping output arrived up to 10s later and was routed from
   selectedPrivateChatPeer at callback time, misrouting the result after a
   chat switch. The origin conversation is now captured when the command is
   issued (CommandOutputDestination) and deferred output is routed there:
   a DM result lands in the origin chat's history even if deselected, and a
   mesh-timeline result pins to #mesh instead of the active channel.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* App Info: move NETWORK section under HOW TO USE and uppercase NETWORK/SYMBOLS headers

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Conform DiagnosticsMockContext to sendPublicMessage

CommandContextProvider gained sendPublicMessage (Cashu /pay, #1376) after
this branch forked, so the diagnostics test mock no longer conformed once
main was merged in. Add the no-op stub.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

bitchat/App/AppChromeModel.swift

@@ -62,6 +62,28 @@ final class AppChromeModel: ObservableObject {
         isAppInfoPresented = true
     }
 
+    /// Builds the mesh topology map model from the transport's gossiped
+    /// graph plus the live nickname table. Unknown nodes (heard about via a
+    /// neighbor claim but never announced to us) fall back to a short ID.
+    func meshTopologyDisplayModel() -> MeshTopologyDisplayModel {
+        let mesh = chatViewModel.meshService
+        guard let snapshot = mesh.currentMeshTopology() else { return .empty }
+        let nicknames = mesh.getPeerNicknames()
+
+        let nodes = snapshot.nodes.map { peerID -> MeshTopologyDisplayModel.Node in
+            let isSelf = peerID == snapshot.localPeerID
+            let label: String
+            if isSelf {
+                label = chatViewModel.nickname
+            } else {
+                label = nicknames[peerID] ?? "\(peerID.id.prefix(8))…"
+            }
+            return MeshTopologyDisplayModel.Node(id: peerID.id, label: label, isSelf: isSelf)
+        }
+        let edges = snapshot.edges.map { ($0.a.id, $0.b.id) }
+        return MeshTopologyDisplayModel(nodes: nodes, edges: edges)
+    }
+
     func triggerScreenshotPrivacyWarning() {
         showScreenshotPrivacyWarning = true
     }