Add mic mode (beta): play without MIDI via microphone pitch detection

[isc]

Prototype for the "Mode micro (non MIDI)" roadmap item: detect played notes through the microphone so acoustic pianos and keyboards without MIDI can use the app.

How it works

• A 🎤 Mic mode button in the score-page topbar (shown when no MIDI keyboard is connected) toggles listening. The "no MIDI devices" help modal also offers mic mode as an alternative.
• micInput.js captures the raw microphone signal (getUserMedia with voice processing disabled) and analyses ~40 ms frames from a 4096-sample AnalyserNode window.
• Pitch detection reuses a proven brick instead of hand-rolled DSP: pitchy 4.1.0 (McLeod Pitch Method, MIT), vendored as a self-contained 9 KB ESM bundle like the project's other vendor libs. This follows a state-of-the-art review: classic DSP (MPM/YIN) remains the standard for low-latency monophonic detection in the browser; neural options (CREPE/SPICE) are heavier for marginal gain, and polyphonic models (Onsets and Frames, Basic Pitch) are offline-transcription oriented.
• pitchDetection.js wraps pitchy with a clarity threshold and a piano-range gate (capped below C8 so a stray detection can never trigger the C8 navigate-back key), converts frequency to MIDI, and runs a debounced note-tracker state machine (2 consistent frames to fire Note On, 3 missing frames to release).
• Detected notes are emitted as synthetic MIDI Note On/Off messages through the existing parseMidiMessage path (same as cassette replay), so free play, training mode, strict mode, reinforcement and cassette recording all work unchanged.

Scope / limitations (prototype)

• Monophonic only: one note at a time — melodies, Hanon, hands-separate practice. Chords are not recognised; the UI labels the mode as beta and the tooltips say so.
• Polyphony remains the roadmap's open question; the ROADMAP entry is updated to point at transcription-model approaches (Onsets and Frames / Basic Pitch) as the next step.
• Velocity is a rough loudness mapping (validation ignores it; it only feeds recordings).

Tests & verification

• 17 new vitest unit tests (test/js/pitchDetection.test.js): pure sines, harmonic-rich piano-like tones (octave-error trap), low notes (A1 semitone resolution), noise/silence rejection, above-range rejection, and the note-tracker debounce/release/flush state machine. Full JS suite: 102/102 pass.
• End-to-end check in headless Chromium with a stubbed 440 Hz mic stream: clicking 🎤 produces exactly one synthetic Note ON: A4 and one Note OFF: A4 through the real app pipeline, no wrong notes, and toggling off restores the idle state.
• Ruby suite locally: 0 assertion failures; 46 errors are all sandbox-environment network timeouts on the pre-existing esm.sh/@tonejs/piano import (unrelated to this diff — CI should be authoritative).

Also in this PR

• Bilingual changelog entry ("Nouveautés" modal) and FR/EN locale strings.
• ROADMAP: the mic-mode idea is replaced by its remaining unknown (polyphony).

🤖 Generated with Claude Code

https://claude.ai/code/session_01TZWBasTr1z9EaDUJdD8V3z

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