- Introduce `RoleLabelDisplay` enum (inline, above, none) and integrate it into UI rendering and message formatting.
- Replace `show_role_labels` boolean with `role_label_mode` across config, formatter, session, and TUI components.
- Add `syntax_highlighting` boolean to UI settings with default `false` and support in message rendering.
- Update configuration schema version to 1.3.0 and provide deserialization handling for legacy boolean values.
- Extend theme definitions with code block styling fields (background, border, text, keyword, string, comment) and default values in `Theme`.
- Adjust related modules (`formatting.rs`, `ui.rs`, `session.rs`, `chat_app.rs`) to use the new settings and theme fields.
- Detect terminal color support and automatically switch to the new `ansi_basic` theme when only 16‑color support is available.
- Introduce `OfflineProvider` that supplies a placeholder model and friendly messages when no providers are reachable, keeping the TUI usable.
- Add `CONFIG_SCHEMA_VERSION` (`1.1.0`) with schema migration logic and default handling in `Config`.
- Update configuration saving to persist the schema version and ensure defaults.
- Register the `ansi_basic` theme in `theme.rs`.
- Extend `ChatApp` with `set_status_message` to display custom status lines.
- Update documentation (architecture, Vim mode state machine) to reflect new behavior.
- Add async‑trait and futures dependencies required for the offline provider implementation.
