feat(updater): auto-upgrade Homebrew installs via brew upgrade

Homebrew-installed versions now automatically run `brew upgrade openboot`
when a newer version is available in the cached update state.
HOMEBREW_NO_AUTO_UPDATE=1 is set to avoid a slow full brew update.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: fullstackjam

internal/updater/updater.go

@@ -98,6 +98,7 @@ func AutoUpgrade(currentVersion string) {
 	}
 
 	if IsHomebrewInstall() {
+		homebrewAutoUpgrade(currentVersion)
 		return
 	}
 
@@ -290,7 +291,11 @@ var execBrewUpgrade = func(formula string) error {
 
 func homebrewAutoUpgrade(currentVersion string) {
 	state, err := LoadState()
-	if err != nil || !state.UpdateAvailable || !isNewerVersion(state.LatestVersion, currentVersion) {
+	if err != nil {
+		checkForUpdatesAsync(currentVersion)
+		return
+	}
+	if !state.UpdateAvailable || !isNewerVersion(state.LatestVersion, currentVersion) {
 		checkForUpdatesAsync(currentVersion)
 		return
 	}

internal/updater/updater_test.go

@@ -372,10 +372,12 @@ func TestHomebrewAutoUpgrade_UpdateAvailable_Failure(t *testing.T) {
 		UpdateAvailable: true,
 	}))
 
+	called := false
 	origExec := execBrewUpgrade
-	execBrewUpgrade = func(formula string) error { return fmt.Errorf("brew failed") }
+	execBrewUpgrade = func(formula string) error { called = true; return fmt.Errorf("brew failed") }
 	defer func() { execBrewUpgrade = origExec }()
 
-	// should not panic
 	homebrewAutoUpgrade("1.0.0")
+
+	assert.True(t, called, "brew should have been called even when it fails")
 }