feat: Formant Envelope Follower

[ford442]

Added an Envelope Follower that modulates the Formant Shift amount dynamically based on the vocal amplitude envelope. Implemented via a native Web Audio sidechain follower circuit (WaveShaperNode -> BiquadFilterNode -> GainNode) within FormantShifter.ts. Exposed formantEnvFollower parameter globally and per-step to the UI via SamplerPanel and NoteSelector. Wired it down through useAudioEngine.ts and SingingVoice.ts to dynamically modulate the formant detune amount based on the vocal amplitude envelope.

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PR created automatically by Jules for task 714986474099753320 started by @ford442

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: f2ba50ce-41b5-4449-8182-a082209e05e3

📥 Commits

Reviewing files that changed from the base of the PR and between 54b63c3 and 85cb1c7.

⛔ Files ignored due to path filters (1)

• pnpm-lock.yaml is excluded by !**/pnpm-lock.yaml

📒 Files selected for processing (15)

• agent_plan.md
• package.json
• patch_brace_correct.py
• patch_brace_final.py
• patch_mock6.py
• src/__tests__/SamplerPanel.perf.test.tsx
• src/components/NoteSelector.tsx
• src/components/SamplerPanel.tsx
• src/components/appParts/ContextMenuNode.tsx
• src/engines/SingingVoice.ts
• src/engines/rubberband/FormantShifter.ts
• src/hooks/audioEngine/audioPlayback.ts
• src/hooks/useAppState.tsx
• src/hooks/useAudioEngine.ts
• src/types.ts

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• Create PR with unit tests
• Commit unit tests in branch feat/formant-envelope-follower-714986474099753320

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