feat: redesign mixer effect chain browser

[ChuxiJ]

Summary

• redesign the mixer effect chain panel with a categorized add-device browser, clearer signal-flow visuals, and more structured device cards
• add drag-and-drop reordering feedback and richer device controls for bypass, presets, wet mix, and removal
• add store-level regression tests covering effect add, reorder, remove, and bypass flows

Scope

This PR intentionally includes only the effect chain browser and device-chain interaction work from the preserved local WIP branch.

The remaining synth and mixer experiments were intentionally left out of this PR because they are not yet integrated cleanly with the current main store/types surface.

Why

The preserved local WIP branch had drifted behind main and contained a mixed set of partial mixer and synth changes. This PR extracts the coherent, shippable effect-chain subset so it can be reviewed independently.

Validation

• ./node_modules/.bin/tsc --noEmit
• ./node_modules/.bin/vitest run src/components/mixer/__tests__/DeviceChainView.test.tsx
• npm run build

[ChuxiJ]

Triage: Review needed — Mixer effect chain browser redesign. Good UX improvement but touches mixer UI. Should be reviewed carefully for interaction design compliance.

---

Generated by Claude Code