e1608: cosmetic minors -- 2-digit frequency spin, smaller mock catch-up cap, docs wording

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/mock_e1608.py

@@ -263,7 +263,7 @@ class Board:
                             self.streaming = False
                     self.log("OVERRUN")
                     return
-                due = min(int((now - t0) * rate) - sent, 65536)
+                due = min(int((now - t0) * rate) - sent, 4096)
                 if due > 0:
                     t = np.arange(sent, sent + due) / rate
                     cols = [self.raw(w, r, t) for (w, r) in queue]