refactor: remove TerminalUI dependency from highlighters

Instead of checking TerminalUI state to skip drawing the primary cursor,
users can now set PrimaryCursor and PrimaryCursorEol faces to default,default
to achieve the same effect. This approach:

- Removes coupling between highlighters and TerminalUI
- Gives users more control over cursor appearance
- Keeps highlighting system focused on its core responsibility
- Opens door for more effects based on primary cursor face

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

Co-Authored-By: Claude <[email protected]>

Author: Yukaii

src/highlighters.cc

@@ -16,7 +16,6 @@
 #include "regex.hh"
 #include "register_manager.hh"
 #include "string.hh"
-#include "terminal_ui.hh"
 #include "utf8.hh"
 #include "utf8_iterator.hh"
 #include "window.hh"
@@ -1291,20 +1290,11 @@ void highlight_selections(HighlightContext context, DisplayBuffer& display_buffe
         highlight_range(display_buffer, begin, end, false,
                         apply_face(sel_faces[primary ? 0 : 1]));
     }
-    // Check if we should skip drawing the primary cursor (for terminal cursor native mode)
-    const bool skip_primary_cursor = TerminalUI::has_instance() &&
-                                     TerminalUI::instance().is_cursor_native();
-
     for (size_t i = 0; i < selections.size(); ++i)
     {
         auto& sel = selections[i];
         const BufferCoord coord = sel.cursor();
         const bool primary = (i == selections.main_index());
-
-        // Skip drawing primary cursor if terminal_cursor_native is enabled
-        if (primary && skip_primary_cursor)
-            continue;
-
         const bool eol = buffer[coord.line].length() - 1 == coord.column;
         highlight_range(display_buffer, coord, buffer.char_next(coord), false,
                         apply_face(sel_faces[2 + (eol ? 2 : 0) + (primary ? 0 : 1)]));