Use existing WaveSurfer player and melt-ui sliders in tag generator

Commit notes

Refactor the producer tag generator UI to reuse the project's existing audio/UX components instead of bespoke ones, for a consistent experience:

- Playback and waveform display now go through the shared Waveform (WaveSurfer) component. Each FX change re-renders the tag to a WAV blob URL that WaveSurfer loads, so the waveform and playback always reflect the applied effects — and the global audio coordinator ensures only one tag plays at a time, like the rest of the app. - FX controls now use a melt-ui Slider builder via a small reusable FxSlider component, matching how the rest of the app builds interactive primitives. - Aligned button/card/input styling with app conventions (hover:bg-brand-500, rounded-lg cards, neutral surfaces).

Co-Authored-By: Claude Opus 4.8 <[email redacted]> Claude-Session: [private session redacted]