docs: apply brand to README and public site #42

Parent

Part of #40.

What to build

Refresh the README as the concise project entry point and align it with the public documentation site. Readers can understand the implemented product, get started, configure authentication, and find detailed guidance without duplicating the full reference site.

Acceptance criteria

• README uses the generated banner and approved tagline: “Download HTTP/HLS streams as MP4 or MKV — no transcoding.”
• README opens with a concise product explanation and highlights implemented capabilities only.
• README provides prerequisites and a clear quick start using the supported Docker and Taskfile workflow.
• README includes a minimal manifest example and explains environment-based header and cookie authentication without exposing credentials.
• README summarizes supported HTTP/HTTPS inputs, MP4/MKV outputs, retries, saved progress, and the default inactivity timeout using verified current behavior.
• README links to detailed public documentation and the project's contributing, support, security, conduct, and license information.
• README avoids duplicating detailed reference content that belongs on the public site.
• README, public documentation, and linked navigation contain no emoji characters.
• Public documentation content moves from the current location to website/; internal engineering material remains in docs/.
• Zensical configuration, documentation checks, and GitHub Pages deployment workflow use the public content location.
• Site styling uses Catppuccin Macchiato with Sky #91d7e3 accent and generated brand assets.
• Pages remain dark-first, responsive, and accessible, with readable contrast and appropriate text alternatives.
• Public content clearly distinguishes implemented capabilities from planned work.
• The pinned Zensical release builds the site successfully; existing documentation quality checks pass.
• GitHub repository description accurately summarizes implemented product behavior.
• GitHub repository topics classify the actual language, protocols, formats, and runtime without implying unimplemented features.
• GitHub repository homepage points to the public documentation site.