fix: Add effective_project_template() to fallback to bundled template

- Add effective_project_template() method that checks if saved template path exists
- If not, falls back to default_project_template() (bundled template)
- This handles users who have old config.json pointing to deleted Cookiecutters path
- Update project.rs to use effective_project_template() when creating new projects

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

src/config.rs

@@ -427,6 +427,17 @@ impl Config {
         }
     }
 
+    /// The project template path to use, falling back to the bundled template
+    /// if the saved path doesn't exist.
+    pub fn effective_project_template(&self) -> PathBuf {
+        // If the saved template path exists and has cookiecutter.json, use it
+        if self.project_template.join("cookiecutter.json").is_file() {
+            return self.project_template.clone();
+        }
+        // Otherwise fall back to the bundled template
+        default_project_template()
+    }
+
     pub fn load() -> Config {
         let path = config_path();
         match std::fs::read_to_string(&path) {