Move playground state and effects into React and Jotai

[skratchdot]

Move playground state and lifecycle coordination into React and Jotai. Components now consume the document-scoped Jotai Provider directly, and playground actions come from React context. Settings, custom algorithms, playback preferences, and visualization choice survive client-side navigation while Home's audio and worker resources are disposed.

Changes:

• Replace the module-level vanilla store, explicit store props, and custom snapshot subscriptions with Jotai hooks and player-state atoms.
• Replace the playground controller and three settings subscription controllers with usePlayers and useSort. React effects own audio setup, settings synchronization, sample preloading, worker cancellation, and edit debouncing.
• Keep transport and synthesis as imperative audio adapters. Audio callbacks read current provider state without subscribing; player callbacks publish into atoms. Cleanup releases recorded frames and ignores late callbacks.
• Preserve immediate page-hide suspension and handle batched hide/show events without leaving cancelled work or open dialogs behind. Restore current settings without automatically starting playback.
• Move player and MIDI helpers into their domain folders, use a React ref for the preview canvas, and update the architecture documentation.
• Enable Oxlint's React hook-order and effect-dependency checks. Add Vitest Browser Mode coverage in real Chromium using React Testing Library in place of the removed controller subscription tests, plus navigation regression coverage.

Validation:

• pnpm run check: lint, formatting, spelling, TypeScript, 353 tests, and production build pass.
• Full Playwright suite: 43 tests pass, including accessibility, editor loading/failures, built-in and custom algorithms, no-Worker fallback, waveform/soundfont controls, playback, MIDI export, navigation, and page lifecycle cleanup.
• Vitest runs Node and Chromium projects through pnpm test; both CI workflows install Chromium before checks. jsdom is not installed. Loop controls update their atom directly instead of passing through the action context.
• Hook tests cover provider isolation, Strict Mode cleanup, focused settings effects, stale worker replies, edit debouncing, suspension, autoplay, and late player callbacks.
• git diff --check passes.

Audio synthesis and transport algorithms are unchanged. Automated checks exercise their integration; no new listening comparison was performed.