docs: six pages get a real film instead of a six-second clip

Product launch, colour grading, faceless explainer, captions and recuts, motion
graphics, and voice and audio.

Five of these led with a six-to-eight second teaser. A six-second clip on the
page that teaches you to make explainers does not teach anything — it is a
placeholder that looks like content. Colour grading, the most visual feature in
the product, had no video at all.

The new films are 34 to 41 seconds and each shows a RANGE rather than one look:
four ways to tell the same idea with no footage; five caption treatments on one
untouched clip; correction, presets, curves, selective colour, all four scopes
and a LUT; narration with music ducking under it and effects on the beat. The
launch film is built by running the workflow on huly.io for real, so the page
that sells the workflow is showing its actual output.

They share one visual system, measured from HyperFrames own light-theme launch
films rather than invented: bone field, near-black type, coral accent, and the
product always a dark panel inset on the light field. Every one carries audio at
about -20 dB and is 1-2 MB.

The old teasers are removed from the three pages where they became a duplicate.
They stay in the workflow picker, which is where a six-second tile belongs.

Guides with nothing to look at: 15 at the start of this work, 5 now.

docs/guides/voice-and-audio.mdx

@@ -25,6 +25,15 @@ understand or feel the video.
   />
 </Frame>
 
+<DocsVideo
+  title="Narration, music ducking under it, and effects landing on the beat"
+  src="https://static.heygen.ai/hyperframes-oss/docs/images/showcase/voice-audio-demo-v1.mp4"
+  poster="https://static.heygen.ai/hyperframes-oss/docs/images/showcase/voice-audio-demo-v1.jpg"
+/>
+
+Turn the sound on for this one — the audio is the subject. You can watch the
+music duck as narration arrives and see each effect land against the waveform.
+
 ## Create a voiceover
 
 Give the agent the approved wording and useful voice direction: