feat: add project output routing controls

[grazzolini]

Summary

• Add project, stem, and cue output controls to Playback and Studio, showing inherited routes, preferred devices, and effective fallback.
• Keep choices inside the rails and responsive Practice Controls drawer, with keyboard focus, Escape, and pointer-leave behavior.
• Update the product docs, changelog, and deterministic release-media catalog.

Motivation

Refs #505. Layer 3 of 3, above #575 and #574. The complete stack is on feat/output-routing-ui for integration testing. Device-clock synchronization, drift correction, latency compensation, and per-output volume remain outside this routing scope.

Testing

• CI workflow passed. Full pnpm lint, pnpm typecheck, and pnpm test passed: 1,035 desktop, 543 Tauri, and 888 backend tests, plus script suites. Native audio's focused 233 tests and cargo check passed.
• Focused UI tests (126) and release-media catalog tests (20) passed. Synthetic browser QA verified selector geometry, lyrics separation, responsive drawers, keyboard focus, and pointer behavior.
• node scripts/capture-release-media.mjs --run generated all 22 catalog items. Visual review found the existing tuner screenshot and video scene crop the frequency readout; routing media passed review.
• Manual validation pending: macOS, Android, and Linux using pnpm dev and installed packages.

Checklist

• Conventional Commit title, product docs, and [Unreleased] changelog updated
• No secrets or copyrighted audio added
• Assembled-stack automated gates and full synthetic capture completed
• Tuner media framing follow-up
• Three-platform development and installed-package testing

The merge-base changed after approval.