docs: Update all references from old 05-Plot/06-First Draft to merged 05-First Draft

- Update project_template test to verify old directories are NOT created
- Update hover text and comments in project.rs
- Update comments and code in file_list.rs
- Update comment in spelling.rs
- Add test assertions to verify 05-Plot and 06-First Draft don't exist in new projects

This ensures all code references match the merged directory structure where
planning and draft content are combined in 05-First Draft with YAML frontmatter.

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

src/app/spelling.rs

@@ -196,7 +196,7 @@ impl App {
 
     /// The project's character folder, looked for beside the workspace and then
     /// up through its ancestors — in a snowflake project the workspace is
-    /// `06-First Draft` and the sheets are its sibling `03-Characters`.
+    /// `05-First Draft` and the sheets are its sibling `03-Story-Bible`.
     pub(super) fn characters_dir(&self) -> Option<PathBuf> {
         /// How far up to look before giving up; deep enough for the layout,
         /// shallow enough not to wander into the home directory.