Enable the Bedrock setup wizard by default (#56033)

## What changed

Promote `bedrock_setup_wizard` to stable and enable it by default for eligible onboarding. Users can still disable it with `features.bedrock_setup_wizard = false`.

## Testing

Update onboarding coverage to check the enabled default and explicit opt-out. Remove the explicit opt-in from daemon startup tests so they exercise the default configuration.

GitOrigin-RevId: 5bd911088681a31d34aa444398e6d3f7d1d87955

codex-rs/features/src/lib.rs

@@ -2017,8 +2017,8 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::BedrockSetupWizard,
         key: "bedrock_setup_wizard",
-        stage: Stage::UnderDevelopment,
-        default_enabled: false,
+        stage: Stage::Stable,
+        default_enabled: true,
     },
     FeatureSpec {
         id: Feature::Personality,