Fix mobile viewport layout on song detail page

[tacticalnoot]

Motivation

• Mobile browsers with dynamic toolbars were hiding the song detail content because the page relied on 100vh; the container should prefer small-viewport units and top-align on mobile so content remains visible and scrollable.

Description

• Update src/pages/[id].astro page wrapper to prefer svh with a vh fallback and change mobile alignment to justify-start while preserving lg:justify-center for large screens (layout-only change).

Testing

• Ran pnpm check (Svelte typecheck); the command ran but failed due to pre-existing TypeScript/Svelte errors unrelated to this layout change (svelte-check reported 21 errors and 12 warnings across other components).

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Codex Task

[cloudflare-workers-and-pages]

Deploying smol-fe with    Cloudflare Pages

Latest commit:	e2ea659
Status:	⚡️  Build in progress...

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