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/config.rs

@@ -1,8 +1,11 @@
 use crate::ProviderConfig;
 use crate::Result;
 use crate::mode::ModeConfig;
+use crate::ui::RoleLabelDisplay;
+use serde::de::{self, Deserializer, Visitor};
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
+use std::fmt;
 use std::fs;
 use std::path::{Path, PathBuf};
 use std::time::Duration;
@@ -11,7 +14,7 @@ use std::time::Duration;
 pub const DEFAULT_CONFIG_PATH: &str = "~/.config/owlen/config.toml";
 
 /// Current schema version written to `config.toml`.
-pub const CONFIG_SCHEMA_VERSION: &str = "1.2.0";
+pub const CONFIG_SCHEMA_VERSION: &str = "1.3.0";
 
 /// Core configuration shared by all OWLEN clients
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -700,8 +703,13 @@ pub struct UiSettings {
     pub word_wrap: bool,
     #[serde(default = "UiSettings::default_max_history_lines")]
     pub max_history_lines: usize,
-    #[serde(default = "UiSettings::default_show_role_labels")]
-    pub show_role_labels: bool,
+    #[serde(
+        rename = "role_label",
+        alias = "show_role_labels",
+        default = "UiSettings::default_role_label_mode",
+        deserialize_with = "UiSettings::deserialize_role_label_mode"
+    )]
+    pub role_label_mode: RoleLabelDisplay,
     #[serde(default = "UiSettings::default_wrap_column")]
     pub wrap_column: u16,
     #[serde(default = "UiSettings::default_show_onboarding")]
@@ -712,6 +720,8 @@ pub struct UiSettings {
     pub scrollback_lines: usize,
     #[serde(default = "UiSettings::default_show_cursor_outside_insert")]
     pub show_cursor_outside_insert: bool,
+    #[serde(default = "UiSettings::default_syntax_highlighting")]
+    pub syntax_highlighting: bool,
 }
 
 impl UiSettings {
@@ -727,8 +737,8 @@ impl UiSettings {
         2000
     }
 
-    fn default_show_role_labels() -> bool {
-        true
+    const fn default_role_label_mode() -> RoleLabelDisplay {
+        RoleLabelDisplay::Above
     }
 
     fn default_wrap_column() -> u16 {
@@ -750,6 +760,62 @@ impl UiSettings {
     const fn default_show_cursor_outside_insert() -> bool {
         false
     }
+
+    const fn default_syntax_highlighting() -> bool {
+        false
+    }
+
+    fn deserialize_role_label_mode<'de, D>(
+        deserializer: D,
+    ) -> std::result::Result<RoleLabelDisplay, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct RoleLabelModeVisitor;
+
+        impl<'de> Visitor<'de> for RoleLabelModeVisitor {
+            type Value = RoleLabelDisplay;
+
+            fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                f.write_str("`inline`, `above`, `none`, or a legacy boolean")
+            }
+
+            fn visit_str<E>(self, v: &str) -> std::result::Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                match v.trim().to_ascii_lowercase().as_str() {
+                    "inline" => Ok(RoleLabelDisplay::Inline),
+                    "above" => Ok(RoleLabelDisplay::Above),
+                    "none" => Ok(RoleLabelDisplay::None),
+                    other => Err(de::Error::unknown_variant(
+                        other,
+                        &["inline", "above", "none"],
+                    )),
+                }
+            }
+
+            fn visit_string<E>(self, v: String) -> std::result::Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                self.visit_str(&v)
+            }
+
+            fn visit_bool<E>(self, v: bool) -> std::result::Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                if v {
+                    Ok(RoleLabelDisplay::Above)
+                } else {
+                    Ok(RoleLabelDisplay::None)
+                }
+            }
+        }
+
+        deserializer.deserialize_any(RoleLabelModeVisitor)
+    }
 }
 
 impl Default for UiSettings {
@@ -758,12 +824,13 @@ impl Default for UiSettings {
             theme: Self::default_theme(),
             word_wrap: Self::default_word_wrap(),
             max_history_lines: Self::default_max_history_lines(),
-            show_role_labels: Self::default_show_role_labels(),
+            role_label_mode: Self::default_role_label_mode(),
             wrap_column: Self::default_wrap_column(),
             show_onboarding: Self::default_show_onboarding(),
             input_max_rows: Self::default_input_max_rows(),
             scrollback_lines: Self::default_scrollback_lines(),
             show_cursor_outside_insert: Self::default_show_cursor_outside_insert(),
+            syntax_highlighting: Self::default_syntax_highlighting(),
         }
     }
 }
@@ -919,7 +986,9 @@ mod tests {
 
     #[test]
     fn expand_provider_env_vars_resolves_api_key() {
-        std::env::set_var("OWLEN_TEST_API_KEY", "super-secret");
+        unsafe {
+            std::env::set_var("OWLEN_TEST_API_KEY", "super-secret");
+        }
 
         let mut config = Config::default();
         if let Some(ollama) = config.providers.get_mut("ollama") {
@@ -935,12 +1004,16 @@ mod tests {
             Some("super-secret")
         );
 
-        std::env::remove_var("OWLEN_TEST_API_KEY");
+        unsafe {
+            std::env::remove_var("OWLEN_TEST_API_KEY");
+        }
     }
 
     #[test]
     fn expand_provider_env_vars_errors_for_missing_variable() {
-        std::env::remove_var("OWLEN_TEST_MISSING");
+        unsafe {
+            std::env::remove_var("OWLEN_TEST_MISSING");
+        }
 
         let mut config = Config::default();
         if let Some(ollama) = config.providers.get_mut("ollama") {