Walkthroughs: stop autoplaying muted, and show the length

Marty asked why they start muted. Browsers only permit autoplay when a video
is muted, so "expand and play" necessarily meant "expand and play silently" —
and for these that is the wrong trade, because the narration IS the training.
A member's first visit was showing them a silent walkthrough.

So the panel now opens paused with the play button showing. Pressing it is a
user gesture, which means it plays with sound, every time. preload stays
'none' until the panel opens, then goes to 'metadata' so an open panel shows
a real first frame instead of a black rectangle.

Each bar now also carries its runtime ("· 71 sec"), so nobody has to guess
whether they are committing to one minute or ten.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

public/suite-split.html

@@ -83,6 +83,6 @@
   <p class="s-note"><strong style="color:var(--text)">Why this is deliberately slow to declare a winner:</strong> click rates on display advertising are small, so a two- or three-click gap on a few hundred impressions is noise, not a result. This tool waits until one version is clearly ahead before it calls anything — and when the versions genuinely tie, it says so, because that is useful information too: it means the wording isn't what's holding the ad back. <br><br>Independent team resource · No income is guaranteed · Cryptocurrency involves risk.</p>
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