Web replay playback flickers (full-screen redraw each frame)

[mparrett]

Playing back a run via ?replay=<code> on the web build works — but the terminal does a full redraw each frame, so it flickers noticeably during playback.

Minor: playback is correct, it's purely visual. The replay path likely clears + repaints the whole screen each frame; a diff/partial redraw (or double-buffer) on playback would remove the flicker.

Context: first end-to-end confirmation that ?replay= playback works on the web build (v0.0.2 candidate).

[mparrett]

The fix here is #151 (incremental redraw during replay playback) — it stops play-replay from blanking the whole screen each frame, which is the root cause.

(Correcting an earlier note of mine that pointed at #149 — that was wrong. #149 predates the fix and still carries this bug; it was only useful as a "before" baseline when A/B-testing #151.)

Closes when #151 merges.