Reorganize source into components, controllers, and domain modules

[skratchdot]

Summary

Reorganize the source tree to make UI, application coordination, and domain logic easier to find. This is a structural refactor, not a redesign or state/API rewrite.

Structure

• Keep Home, About, and API content directly in TanStack route files. Route components remain unexported so automatic code splitting can work.
• Group screen controls under components/playground, dialogs under components/dialogs, and the document shell under components/layout.
• Replace the generic workspace terminology with playground and player names, including the screen DOM ID and lazy-load error message.
• Move non-React orchestration into controllers while leaving shared state in state.
• Consolidate lib/utilities into utils with function-specific filenames and update shadcn aliases.
• Move the worker into sorting, the Timbre adapter into audio, and audio preview drawing into audio. Keep editor initialization beside its dialog.
• Update imports, browser selectors, tests, and developer documentation.

Behavior preserved

Browser-only audio/editor loading, prerendering, navigation, worker execution, editing, playback lifecycle, and the current visual design are retained. No React Compiler or new hooks layer is introduced.

Verification

• pnpm run check passed: lint, formatting, spelling, TypeScript, 360 unit tests, and production build.
• All 37 Playwright browser tests passed using local Chrome.
• About and API remain separate production chunks; all three pages prerender successfully.
• git diff --check passed.
• Existing large-chunk build warnings remain. Edit-time Fast Refresh state preservation was not separately tested.