feat(cli): preserve leading numeric prefixes in Blume group slugs

apps/cli/sync.ts

@@ -475,7 +475,14 @@ for (const sol of ordered) {
   // An unplanned problem's category may share a folder with a numbered topic
   // (`Hash Table` warm-ups under topic 1); the numbered one owns the meta.
   const topic = topics.get(sol.num) ?? { name: sol.category };
-  const group = topic.name.toLowerCase().replace(/[^a-z0-9]+/g, "-").replace(/^-|-$/g, "");
+  // Blume reads a leading `<digits>-` on a folder as a sidebar-order prefix and
+  // strips it from the route (`1-d-…` → `/d-…`), so a slug that would start that
+  // way keeps the digits glued to the next token (`1d-dynamic-programming`).
+  const group = topic.name
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/^-|-$/g, "")
+    .replace(/^(\d+)-/, "$1");
   if (groups.get(group)?.order === undefined) groups.set(group, topic);
   const name = `${group}/${sol.num}-${sol.slug}.mdx`;
   const existing = pages.get(sol.num);