Docs: Add an interactive Jetpack homepage hero

[f]

Fixes #

Proposed changes

• Progressively enhance the mapped Jetpack Developer Docs homepage hero with an interactive Three.js technical drawing.
• Let pointer users drag individual geometry points while connected strokes deform and spring back after release.
• Support light and dark theme colors, reduced motion, responsive sizing, and an image fallback when WebGL or the module is unavailable.
• Remove the legacy hero grid, column divider, visual overlay, and adjacent separator on this site only.
• Remove the WordPress resource links, Jetpack.com developer-post feed, and agent-oriented prompt sections from the homepage.

Related product discussion/links

• N/A

Does this pull request change what data or activity we track or use?

No.

Testing instructions

• Run node --test tools/docspress/jetpack-developer-docs-site/tests/*.test.cjs.
• Run php tools/docspress/jetpack-developer-docs-site/tests/render-test.php.
• Package and install the site adapter on the mapped Jetpack Developer Docs site.
• Open the homepage in light mode and confirm the construction lines and annotation labels are clear and proportionate on the white surface.
• Drag inner and outer points and confirm their connected geometry deforms while held, then returns home after release.
• Confirm the original image remains available as the no-JavaScript and module-failure fallback.
• Confirm the homepage flows from Developer tools to Latest updates without the three removed sections.

[github-actions]

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