feat: apply the stackmap brand

[hyamero]

Brings the identity from the stackmap design system into the repo. Stacked on #14, so merge that first.

• Brand assets in assets/brand/ (copied from the design system, not redrawn): the mark and its builds, lockups, wordmark, app icon, favicons, README header and social card. Its README covers when to use each build, the colour rules and the voice.
• README:
  • Opens with the brand header as a light/dark <picture>.
  • The screenshots are re-shot with the one-row header.
  • prepack points the images at GitHub, because npm resolves relative images against the package rather than the repo.
  • The npm description is now the brand descriptor.
• Viewer: the compact-mark favicon is inlined as a data URI, so the file still opens offline. The brand colour stays out of the viewer chrome, as the brand book requires.
• CLI: on a TTY, output starts with a stackmap · <command> line (the name in bold), and the written path or served URL is in the brand accent:
  • Truecolor, 256-colour or basic blue, picked for a light or dark terminal.
  • With NO_COLOR set, the header line prints as plain text and nothing is coloured.
  • Piped output (what agents read) and --json stay byte-identical.

[github-actions]

🎉 This PR is included in version 0.1.0-rc.1 🎉

The release is available on:

• v0.1.0-rc.1
• GitHub release

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[github-actions]

🎉 This PR is included in version 0.1.0 🎉

The release is available on:

• v0.1.0
• GitHub release

Your semantic-release bot 📦🚀