fix: rename typing_current_cursor to typing_cursor_fg in ascii theme

Aligns cursor color field naming with the established theme structure for consistency.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

assets/themes/ascii.json

@@ -23,7 +23,7 @@
     "metrics_stage_info": "blue",
     "typing_untyped_text": "white",
     "typing_typed_text": "light_blue",
-    "typing_current_cursor": "black",
+    "typing_cursor_fg": "black",
     "typing_cursor_bg": "white",
     "typing_mistake_bg": "red"
   },
@@ -48,7 +48,7 @@
     "metrics_stage_info": "blue",
     "typing_untyped_text": "blue",
     "typing_typed_text": "blue",
-    "typing_current_cursor": "white",
+    "typing_cursor_fg": "white",
     "typing_cursor_bg": "black",
     "typing_mistake_bg": "red"
   }