Add 'Copy lyrics' floating button to song detail page

[tacticalnoot]

Motivation

• Provide a quick, discoverable way for visitors to copy a song's lyrics from the song detail page (/[id]) without manually selecting text.

Description

• Add a small floating Copy lyrics button to src/pages/[id].astro that only renders when lyricsDisplay is present and an inline <script is:inline> attaches a click handler which calls navigator.clipboard.writeText and shows transient feedback (Copied / Copy failed).

Testing

• Ran npm run check which runs svelte-check; it completed but reported existing unrelated type errors in other components so the project-wide type check failed (unrelated to this change).
• Attempted npm run lint but the repository does not define a lint script, so linting was not performed.

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Codex Task

[cloudflare-workers-and-pages]

Deploying smol-fe with    Cloudflare Pages

Latest commit:	6cd7a9a
Status:	⚡️  Build in progress...

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