Log header git actions into the session chat

Add a `.note` AgentEvent kind — a system-generated log line — and emit one
into the open session's transcript whenever a control in the header Git menu
is used (merge/squash/rebase outcome, open in Terminal, reveal in Finder,
copy branch/worktree path). Renders as a muted note on both macOS and iOS.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

NucleicRemote/NucleicRemote/Views/TranscriptRow.swift

@@ -35,6 +35,9 @@ struct TranscriptRow: View {
         case .error(let err):
             Label(err.message, systemImage: "xmark.octagon.fill")
                 .font(.caption).foregroundStyle(.red)
+        case .note(let note):
+            Label(note.text, systemImage: note.icon ?? "arrow.triangle.branch")
+                .font(.caption).foregroundStyle(.secondary)
         default:
             EmptyView()
         }