⚡ Bolt: Optimize InstancedMesh matrix updates in audio batchers

[ford442]

Bottleneck: High-frequency update loops in arpeggio-batcher.ts and portamento-batcher.ts were utilizing a dummy THREE.Object3D proxy and calling dummy.updateMatrix() and mesh.setMatrixAt(i, dummy.matrix). This forces Three.js to calculate Euler angles, update local matrices, and process object graph overhead per instance, per frame, causing massive CPU bottlenecking and internal allocation churn.

Fix: Completely bypassed the object proxy for matrix composition. Implemented a zero-allocation "Batcher Sweep" by composing position, quaternion rotation, and scale data directly into a module-level scratch THREE.Matrix4(), then writing it straight to the InstancedMesh's flat Float32Array using _scratchMatrix.toArray(this.mesh.instanceMatrix.array, i * 16). Flagged needsUpdate = true exactly once after the loop.

Impact: Eliminated CPU overhead and garbage collection spikes caused by per-frame object graph traversals and matrix allocations. Drastically improves render loop efficiency and stabilizes framerate for dynamically animated audio-reactive foliage.

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PR created automatically by Jules for task 8322037080807236790 started by @ford442

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