Integrate UI customization documentation into OptiView Player

[jpestugia]

Summary

• reposition Open Video UI as the component-based customization option for OptiView Player
• group UI documentation into Default UI, Open Video UI, and Chromeless approaches
• nest Open Video UI documentation within the relevant Player SDK sections
• provide consistent introductions, getting-started guides, how-to guides, and examples across SDKs
• split oversized chromeless guides into focused component mapping, UX, error handling, and sample pages
• preserve legacy Open Video UI URLs through redirects
• remove the obsolete standalone Open Video UI documentation plugin and supporting configuration

Test plan

• Run Prettier formatting checks
• Run MDX spellcheck
• Run ESLint
• Run TypeScript type checking
• Run the full Docusaurus production build
• Verify Web, Android, iOS/tvOS, React Native, and Roku UI routes locally
• Verify legacy Open Video UI redirects

[MattiasBuelens]

Hmm, the PR preview failed to deploy because it needs a secret that is only available inside this repo, not on a fork... Sorry, we probably should have tested this before we rolled out the new previews. 😕

@jpestugia Could you re-open this PR from a branch on this documentation repository instead? You should have the necessary access now.

[jpestugia]

Recreated from a branch in the THEOplayer/documentation repository as requested: #873. The new preview deployed successfully at https://docs-preview.optiview.dolby.com/pr-873/.