fix(skills): use published HyperShader runtime

[miguel-heygen]

Summary

• replace the website-to-video skill's monorepo-only HyperShader copy command with installation from the published @hyperframes/shader-transitions package
• clarify that registry shader blocks are standalone showcases, not the reusable multi-scene runtime
• add regression coverage for public-install guidance

Reproduction

The published hyperframes@0.7.56 package does not contain packages/shader-transitions/dist/index.global.js. The separately published @hyperframes/shader-transitions@0.7.56 package does contain dist/index.global.js.

Verification

• bunx vitest run packages/cli/src/commands/websiteToVideoSkillContent.test.ts packages/cli/src/utils/skillsManifest.test.ts (57 passed)
• bun run lint:skills
• bun run test:skills (229 passed)
• isolated npm install --no-save --package-lock=false @hyperframes/shader-transitions@0.7.56 and browser-bundle copy (253,625-byte output)