chore(demo): refresh recorded casts, update slides format, and add video pipeline

[GarthDB]

Description

Updates the demo presentation content and video rendering infrastructure:

Cast files (asciinema v2):

• A-find.cast, B-name.cast, C-suggest.cast, D-agent.cast — re-recorded demos with beat markers injected by the automation framework from feat(tui,demo): add layout breakpoint tests, tui-verify skill runner, and rmux automation framework #1107. Each cast is significantly expanded with richer interaction flows.

Slides (tools/demo/presentation/slides.md):

• Reformatted YAML frontmatter for Slidev 4.x compatibility
• Updated poster timestamps (0:00 → 0:02 for cleaner first-frame thumbnails)
• Refined beat narration comments to match new cast content

Video pipeline (tools/demo/videos/):

• render.mjs — conditionally skips VHS when all beats are prerendered; checks for missing prerendered clips
• tape.mjs — adds prerendered boolean typedef for clips generated by the split-cast.py prebuild step
• A-find.demo.mjs, B-name.demo.mjs, C-suggest.demo.mjs, D-agent.demo.mjs — new per-demo beat manifests replacing the previous inline definitions
• lib/split-cast.py — new script that converts an asciinema cast to per-beat MP4 clips via agg (GIF) → ffmpeg (split on marker times)

Related Issue

Accompanies #1107 (rmux automation framework that produced these recordings). Independent of #1106.

Motivation and Context

The cast files were re-recorded using the new automated pipeline from #1107, which produces deterministic recordings with precisely placed beat markers. The video pipeline is updated to consume prerendered beat clips from split-cast.py rather than re-rendering from VHS on every build.

How Has This Been Tested?

• Presentation loads correctly in Slidev dev server
• moon run demo:videos-render completes without errors with the new manifests
• Cast files play back correctly in asciinema player

Screenshots (if appropriate):

N/A

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[changeset-bot]

⚠️ No Changeset found

Latest commit: d2023b4

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[github-actions]

Run report for d2023b48

Total time: 2m 15s | Comparison time: 1m 55s | Estimated loss: 20.4s (15.0% slower)

	Action	Time	Status	Info
🟩	SyncWorkspace	7.2ms	Passed
🟩	SyncProject(demo)	0.3ms	Passed
🟩	RunTask(demo:verify)	2m 15s	Passed	SLOW
🟩	RunTask(demo:ci)	8.8ms	Passed

Touched files

tools/demo/presentation/public/casts/A-find.cast
tools/demo/presentation/public/casts/B-name.cast
tools/demo/presentation/public/casts/C-suggest.cast
tools/demo/presentation/public/casts/D-agent.cast
tools/demo/presentation/slides.md
tools/demo/videos/A-find.demo.mjs
tools/demo/videos/B-name.demo.mjs
tools/demo/videos/C-suggest.demo.mjs
tools/demo/videos/D-agent.demo.mjs
tools/demo/videos/lib/split-cast.py
tools/demo/videos/lib/tape.mjs
tools/demo/videos/render.mjs