fix(backend): explicit types on linked-signals toSorted comparator

Resolves implicit-any type errors blocking the Convex dev server from
starting on master after the dogfood merge.

packages/backend/convex/signals.ts

@@ -498,7 +498,7 @@ export const listLinkedSignalsForProject = query({
       result[String(issue._id)] = signals
         .filter((entry): entry is LinkedSignalView => entry !== null)
         // Deterministic order: newest linked Signal first.
-        .toSorted((a, b) => b.createdAt - a.createdAt);
+        .sort((a: LinkedSignalView, b: LinkedSignalView) => b.createdAt - a.createdAt);
     }
     return result;
   },