## Summary
- enable the remote plugin feature by default
- promote the remote plugin feature from under development to stable
- preserve the existing `features.remote_plugin` override for explicitly
disabling it
- keep legacy disabled-path coverage explicit in TUI and app-server
tests
## Impact
Remote plugin functionality is enabled by default for configurations
that do not set the feature flag. The existing Codex backend
authentication gate still applies.
## Validation
- `just fmt`
- `just test -p codex-features`
- `just test -p codex-tui
plugins_popup_remote_section_fallback_states_snapshot`
- targeted `codex-app-server` plugin-list and skills-list tests
- `git diff --check`
The full TUI and app-server suites were also exercised locally. All
remote-plugin-related coverage passed; unrelated local
sandbox/test-binary failures remain outside this change.