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/AppModel.swift

@@ -43,6 +43,8 @@ public final class AppModel {
     var hotkeyDisplayString: String { captureHotkey.displayString }
     /// Staged update offered in the menu. Set only after checksum + payload validation.
     public private(set) var updateAvailable: (version: String, notes: String)?
+    /// True for the duration of any appcast check (manual or scheduled).
+    public private(set) var isCheckingForUpdates: Bool = false
 
     let paths: AppSupportPaths
     let spool: SpoolStore
@@ -96,8 +98,19 @@ public final class AppModel {
                 self.setStatus(message)
             }
         }
+        self.updateChecker.onCheckingChanged = { [weak self] checking in
+            self?.isCheckingForUpdates = checking
+        }
     }
 
+    /// CFBundleShortVersionString of the running app.
+    public var appVersion: String { UpdateChecker.currentVersion() }
+    /// Version recorded in the app-managed rollback copy, when one exists.
+    public var previousVersion: String? { updateChecker.previousVersion() }
+    /// Most recent status text — shared with the general status line by design
+    /// (Redline has one status channel, not a separate update-only one).
+    public var updateStatusMessage: String? { statusLine }
+
     // MARK: Seam mutators — the only way a WP-4b/4c extension changes state.
 
     func setStatus(_ text: String?) { statusLine = text }
@@ -219,6 +232,19 @@ public final class AppModel {
         updateChecker.installStaged()
     }
 
+    /// User-initiated appcast check ("Check for updates" menu row).
+    public func checkForUpdates() {
+        Task { @MainActor in
+            await updateChecker.checkNow(manual: true)
+        }
+    }
+
+    /// Reverts `/Applications/Redline.app` to the app-managed rollback copy and relaunches.
+    /// Does nothing unless a `Redline.app.previous` exists and the user clicked the row.
+    public func revertToPreviousVersion() {
+        updateChecker.revertToPrevious()
+    }
+
     /// Unregisters `capture` and binds `HotkeyPreference.load()`. If Carbon rejects the new
     /// combo, restores the previous preference (UserDefaults + Carbon) so the old one keeps working.
     func reRegisterHotkey() {