fix missing root breadcrumb on history pages

crates/treehouse/src/generate.rs

@@ -96,6 +96,7 @@ pub struct HistoryPage {
     pub title: String,
     pub commits: Vec<Commit>,
     pub tree_path: String,
+    pub is_history: bool, // always true
 }
 
 #[derive(Serialize)]
@@ -618,6 +619,7 @@ impl Generator {
                         })
                         .collect(),
                     tree_path: tree_path.to_owned(),
+                    is_history: true,
                 },
                 season: Season::current(),
             };