feat(ui): add configurable role label display and syntax highlighting support

- 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.

crates/owlen-core/src/session.rs

@@ -16,7 +16,7 @@ use crate::storage::{SessionMeta, StorageManager};
 use crate::types::{
     ChatParameters, ChatRequest, ChatResponse, Conversation, Message, ModelInfo, ToolCall,
 };
-use crate::ui::UiController;
+use crate::ui::{RoleLabelDisplay, UiController};
 use crate::validation::{SchemaValidator, get_builtin_schemas};
 use crate::{ChatStream, Provider};
 use crate::{
@@ -264,7 +264,7 @@ impl SessionController {
         );
         let formatter = MessageFormatter::new(
             config_guard.ui.wrap_column as usize,
-            config_guard.ui.show_role_labels,
+            config_guard.ui.role_label_mode,
         )
         .with_preserve_empty(config_guard.ui.word_wrap);
         let input_buffer = InputBuffer::new(
@@ -351,6 +351,10 @@ impl SessionController {
         self.formatter.set_wrap_width(width);
     }
 
+    pub fn set_role_label_mode(&mut self, mode: RoleLabelDisplay) {
+        self.formatter.set_role_label_mode(mode);
+    }
+
     // Asynchronous access to the configuration (used internally).
     pub async fn config_async(&self) -> tokio::sync::MutexGuard<'_, Config> {
         self.config.lock().await