feat: add Practice mode — play a tune's part on a real drum and get scored on your timing

[pliski]

This is a proposal — discussion in #150. An unsolicited feature I built for my own use as a beginner drummer, offered upstream in case it helps others.
Opened as a draft alongside #150 so the code is visible, with no assumption it should be merged as-is — I'd value your read on whether it fits the project first.
A live instance my group uses: https://ror-player.quaidubas30.ch (microphone + headphones).

What this adds

A new Practice tab. The user plays one instrument's part on a real drum into their microphone, and RoR Player scores their timing and accuracy against the tune.

How it works

• Onset detection (src/services/onsetDetector*): an AudioWorklet computes RMS energy with an adaptive noise floor and emits an onset per detected drum hit.
• Engine (src/services/practiceEngine.ts): runs a count-in, then loops the tune (your part solo, or the band minus your part) and anchors a per-loop baseline on the real audio loop wrap.
• Scorer (src/services/practiceScorer.ts): matches detected onsets against the expected timeline on an unrolled monotonic loop timeline, yielding per-stroke verdicts and a 0–100 score.
• UI (src/ui/practice/): toolbar (tune/part/instrument/mode), a live score rail with a timing meter, the per-stroke partition highlight, and an acoustic-loopback latency calibration wizard.

How to try it

Open Practice, pick a tune → part → instrument, put on headphones, press
Start, and play along after the count-in. Use ⚙ → Calibrate to measure your
audio latency.

Notes for reviewers

• Needs a microphone and headphones (speaker bleed is counted as your hits).

• The build emits a separately-served onsetDetector.worklet-*.js — AudioWorklet code cannot be inlined.

• New dev-dependency: @types/audioworklet (typings only).

• The Practice i18n namespace is intentionally English-only for now.

• Additive / opt-in: shared components (pattern-player, hybrid-sidebar) gained default-off props, so Listen and Compose are byte-unchanged.

• Companion documentation PR: docs: add Practice mode user guide ror-player-docs#1