Add media-bus video hero block

[somarc]

Summary

• Adds a video-hero block for the demo site.
• Supports DA-authored light/dark video rows and switches the active source on the existing aem-theme-change event.
• Keeps hero MP4 assets in DA media bus instead of Git.

Draft content

• Test page: https://mhess-video-hero-draft--demo--scdemos.aem.page/drafts/mhess/
• Authoring path: /drafts/mhess/index.html
• Main site content is not changed by this PR.

Media bus assets

• Dark: /media/fire-hero-splash.mp4 -> /media/media_186dafa8b9846ad8d38ae6b974842dc7fadbddc2a.mp4
• Light: /media/fire-hero-splash-light.mp4 -> /media/media_18c05a6cf78aa811ab5daa1f7b3dc95eec5c7ae46.mp4

Verification

• Confirmed both stable media paths are DA content-bus owned and return preview 200.
• Confirmed branch code no longer serves the MP4 from Git.
• Confirmed draft page source references both stable media paths.

Notes

• This PR only contains code for the block: blocks/video-hero/video-hero.js and blocks/video-hero/video-hero.css.
• The draft page content was authored in DA under /drafts/mhess/, not committed to Git.

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Commits

• 3da62c5 ✅ (latest)
• 0b65d85 ✅
• c3bc382 ✅
• 95f3427 ✅
• 9238ff0 ✅

[aem-code-sync]

	Page	Scores	Audits	Google
📱	/drafts/mhess/
🖥️	/drafts/mhess/