feat: migrate StageSummaryScreen to ratatui

StageSummaryScreenをratatuiに移行しました。

Changes:
- Migrate StageCompletionView to ratatui
  - Add render() method with proper layout calculation
  - Use GradationText for score ASCII display (completed challenges)
  - Use solid colors for failed/skipped challenges
  - Render title, score label, ASCII score, metrics, progress, and options
- Update StageSummaryScreen to use ratatui backend
- Add snapshot test with MockStageSummaryDataProvider
- Adjust spacing:
  - 3 lines after title
  - 2 lines before metrics (CPM/WPM/Time)
  - Fix vertical centering calculation

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

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

Author: unhappychoice

src/presentation/game/screens/stage_summary_screen.rs

@@ -4,10 +4,12 @@ use crate::presentation::game::events::NavigateTo;
 use crate::presentation::game::screens::ResultAction;
 use crate::presentation::game::views::StageCompletionView;
 use crate::presentation::game::{
-    Screen, ScreenDataProvider, ScreenType, SessionManager, UpdateStrategy,
+    RenderBackend, Screen, ScreenDataProvider, ScreenType, SessionManager, UpdateStrategy,
 };
 use crate::{GitTypeError, Result};
 use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
+use ratatui::Frame;
+use std::io::Stdout;
 use std::sync::{Arc, Mutex};
 
 pub struct StageSummaryData {
@@ -99,6 +101,10 @@ impl Screen for StageSummaryScreen {
         ScreenType::StageSummary
     }
 
+    fn get_render_backend(&self) -> RenderBackend {
+        RenderBackend::Ratatui
+    }
+
     fn default_provider() -> Box<dyn ScreenDataProvider>
     where
         Self: Sized,
@@ -157,7 +163,11 @@ impl Screen for StageSummaryScreen {
         }
     }
 
-    fn render_crossterm_with_data(&mut self, _stdout: &mut std::io::Stdout) -> Result<()> {
+    fn render_crossterm_with_data(&mut self, _stdout: &mut Stdout) -> Result<()> {
+        Ok(())
+    }
+
+    fn render_ratatui(&mut self, frame: &mut Frame) -> Result<()> {
         if let Some(ref stage_result) = self.stage_result {
             // Calculate the stage number that was just completed
             let completed_stage = if self.is_completed {
@@ -171,18 +181,17 @@ impl Screen for StageSummaryScreen {
 
             let has_next = !self.is_completed;
 
-            StageCompletionView::render_complete(
+            StageCompletionView::render(
+                frame,
                 stage_result,
                 completed_stage,
                 self.total_stages,
                 has_next,
                 stage_result.keystrokes,
-            )?;
-
-            Ok(())
-        } else {
-            Ok(())
+            );
         }
+
+        Ok(())
     }
 
     fn get_update_strategy(&self) -> UpdateStrategy {