feat: include Zen challenges in main challenge loading

- Add Zen challenges (entire files) to standard challenge generation
- Fix missing Zen challenges in title screen challenge count
- Zen challenges now appear alongside other difficulty levels

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

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

Author: unhappychoice

src/extractor/repository_loader.rs

@@ -60,10 +60,15 @@ impl RepositoryLoader {
 
         progress.set_step(crate::game::models::loading_steps::StepType::Generating);
         // Expand chunks into multiple challenges across difficulties
-        let challenges = self
+        let mut challenges = self
             .converter
             .convert_chunks_to_challenges_with_progress(chunks, progress);
 
+        // Also add Zen challenges (entire files)
+        let file_paths = self.collect_source_files(repo_path)?;
+        let zen_challenges = self.converter.convert_whole_files_to_challenges(file_paths);
+        challenges.extend(zen_challenges);
+
         progress.set_step(crate::game::models::loading_steps::StepType::Finalizing);
         Ok(challenges)
     }