feat: surface check/revert/version in the menu and badge the icon

AppModel exposes appVersion, previousVersion, isCheckingForUpdates and
updateStatusMessage (an alias for the existing statusLine plumbing — one
status channel, not a new one), plus checkForUpdates() and
revertToPreviousVersion() wired to the hardened UpdateChecker.

Menu gains, in order: "Update to X" (unchanged, staged-only), "Check for
updates" (labelled "Checking…" and disabled mid-check), "Revert to <version>"
(only when a rollback copy exists), then the existing rows unchanged, then a
non-interactive footer "Redline <version>" with the status line under it —
same caption/secondary styles already used elsewhere in the file, no new
tokens.

Menu-bar icon gets a small badge while an update is staged: uses the SF
Symbol's own ".badge" variant when one exists for the current icon, otherwise
overlays a small dot on the plain symbol. Reads live model state, so the
badge disappears on its own once the offer clears.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Sources/Shotdeck/MenuBarView.swift

@@ -15,6 +15,8 @@ struct MenuBarView: View {
                 Divider()
                 returnsBlock
             }
+            Divider()
+            updateFooter
         }
         .padding(10)
         .frame(width: 320, alignment: .leading)
@@ -83,6 +85,21 @@ struct MenuBarView: View {
                 }
             }
 
+            Button {
+                model.checkForUpdates()
+            } label: {
+                actionLabel(model.isCheckingForUpdates ? "Checking…" : "Check for updates")
+            }
+            .disabled(model.isCheckingForUpdates)
+
+            if let previous = model.previousVersion {
+                Button {
+                    model.revertToPreviousVersion()
+                } label: {
+                    actionLabel("Revert to \(previous)")
+                }
+            }
+
             Button {
                 let anchor = NSApp.keyWindow?.contentView
                 if let sender = model as? SendCapable {
@@ -193,4 +210,18 @@ struct MenuBarView: View {
     private var newestReturns: [ReturnedDocument] {
         model.allReturns.sorted { $0.detectedAt > $1.detectedAt }
     }
+
+    private var updateFooter: some View {
+        VStack(alignment: .leading, spacing: 2) {
+            Text("Redline \(model.appVersion)")
+                .font(.caption)
+                .foregroundStyle(.secondary)
+            if let message = model.updateStatusMessage {
+                Text(message)
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+                    .fixedSize(horizontal: false, vertical: true)
+            }
+        }
+    }
 }