feat: Ensure 06-First Draft folder is expanded in file list when opening projects

- Add explicit code in open_workspace to ensure manuscript folder is not collapsed
- Update README to clarify that project root is opened with manuscript folder expanded
- Keep workspace at project root but ensure file list shows 06-First Draft expanded

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

src/app/workspace.rs

@@ -91,6 +91,10 @@ impl App {
         self.load_characters();
         self.autocomplete = None;
         self.collapsed.clear();
+        // Ensure the manuscript folder (e.g., 06-First Draft) is always expanded
+        if let Some(ref dir) = self.manuscript_dir {
+            self.collapsed.remove(dir);
+        }
         if let Some(idx) = first_listed(&self.files, self.manuscript_dir.as_deref()) {
             self.select(idx);
         }