feat: improve output configuration step

[hi-ogawa-agent]

Summary

• replace implementation-first configuration controls with five output radio cards
• move model, shifts, and backing mix into collapsed advanced settings
• default new preferences to subtract-source backing while preserving stored values
• update preference and model-file E2E coverage for the new controls

This ports the output-first UI from hi-ogawa/youtube-audio-replacement#30 to the standalone app while preserving its existing visual language.

Verification

• pnpm build-wasm
• pnpm lint-check
• pnpm -C packages/app test-e2e artifact-store.spec.ts model-files.spec.ts preferences.spec.ts
• pnpm -C packages/app build
• desktop and mobile browser render inspection

The model-backed separation E2E was not run because this checkout has no local data/onnx-lean model fixtures.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	demucs-onnx	8bd4d29	Commit Preview URL Branch Preview URL	Jul 20 2026, 05:35 AM

[pkg-pr-new]

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npm i https://pkg.pr.new/hi-ogawa/demucs-onnx/@hiogawa/demucs-onnx-wasm@69

commit: 8bd4d29