Enhance the input waveform without changing the HUD

[IchenDEV]

Summary

• Keep the existing recording HUD capsule, material, dimensions, spacing, and action-button styling unchanged.
• Replace the seven-bar meter with a smoothed, layered live waveform inside the original 42×14 slot.
• Respect Reduce Motion for both waveform animation and overlay frame transitions.

Why

The recording signal can communicate live audio more clearly, but the established compact capsule is already the stronger visual design. This revision deliberately limits the change to the visualization instead of restyling the surrounding HUD.

Impact

The overlay retains its original 148×40 capsule silhouette and familiar monochrome controls. Only the center audio visualization becomes richer and more responsive.

Validation

• swift test --scratch-path /Users/chenli/projects/opentype/.build — 529 passed, 7 skipped, 0 failed; Swift Testing: 2 passed.
• ./scripts/ci-basic-checks.sh
• Real .app visual QA confirmed the original 148×40 capsule geometry, 42×14 waveform slot, button styling, and accessibility labels.
• codesign --verify --deep --strict dist/OpenType.app
• Temporary visual-preview code was removed from the final source and bundle.