Restore Svelte UI styling by replacing missing utility pipeline with static CSS

[antiero]

Motivation

• The Svelte components still use Tailwind-style utility class names, but the Tailwind pipeline is not running in the deployed build, leaving the UI unstyled and not matching the original React site.
• The intent is to restore the original visual appearance while keeping the Svelte application logic and behavior unchanged.
• Provide a minimal, self-contained stylesheet so the existing class tokens resolve without reintroducing the full Tailwind build pipeline.

Description

• Replaced the @import "tailwindcss" dependency in src/index.css with a self-contained global stylesheet that defines a minimal compatibility layer of utility classes used throughout the Svelte components.
• Preserved the font import and the custom select arrow styling so controls keep their intended appearance.
• No JavaScript, audio, or MIDI logic was changed; only src/index.css was modified to restore layout, spacing, colors, and responsive utility classes.

Testing

• Ran the production build with npm run build, which failed due to a missing optional native Rollup package (@rollup/rollup-linux-x64-gnu) in the environment, so the build could not be validated here; the failure is an environment/dependency issue rather than a code change failure.

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Codex Task