chore: sweep em dashes from our own source and README (#13)

src/lib/thread.ts

@@ -21,7 +21,7 @@ export function buildThread(turns: ChatTurn[], live: LiveState): ThreadMessage[]
   const messages: ThreadMessage[] = [];
 
   // Strictly newest message first. The search bar sits at the top of the window,
-  // so the most recent thing — an answer, once one has been written — should be
+  // so the most recent thing, an answer once one has been written, should be
   // the first line under it. A consequence is that within an exchange the answer
   // comes before its question, which is the intended reading order here.
   for (let index = turns.length - 1; index >= 0; index--) {