feat(ui): add show_cursor_outside_insert setting and Unicode‑aware wrapping; introduce grayscale‑high‑contrast theme

- Added `show_cursor_outside_insert` (default false) to `UiSettings` and synced it from config.
- Cursor rendering now follows `cursor_should_be_visible`, allowing visibility outside insert mode based on the new setting.
- Replaced `textwrap::wrap` with `wrap_unicode`, which uses Unicode break properties for proper CJK and emoji handling.
- Added `grayscale-high-contrast.toml` theme, registered it in theme loading, and updated README and tests.

crates/owlen-core/src/config.rs

@@ -710,6 +710,8 @@ pub struct UiSettings {
     pub input_max_rows: u16,
     #[serde(default = "UiSettings::default_scrollback_lines")]
     pub scrollback_lines: usize,
+    #[serde(default = "UiSettings::default_show_cursor_outside_insert")]
+    pub show_cursor_outside_insert: bool,
 }
 
 impl UiSettings {
@@ -744,6 +746,10 @@ impl UiSettings {
     const fn default_scrollback_lines() -> usize {
         2000
     }
+
+    const fn default_show_cursor_outside_insert() -> bool {
+        false
+    }
 }
 
 impl Default for UiSettings {
@@ -757,6 +763,7 @@ impl Default for UiSettings {
             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(),
         }
     }
 }