Add free producer tag generator lead-gen tool

Commit notes

A public, no-auth page (/tag-generator) that synthesizes five distinct AI voice tags from a producer's phrase and captures their email as a lead — modeled on plugmytag.com. Reuses the existing OpenAI integration.

Backend: - producer-tag service generates 5 hand-tuned voice presets via OpenAI TTS (gpt-4o-mini-tts) using the configured OPENAI_API_KEY / ENABLE_LLM_ANALYSIS. - producer-tag-generator routes: generate (email capture + synthesis), fetch batch, stream dry audio, and MP3/WAV export. IP rate-limited, fails open if Redis is down. - New tables (producer_tag_leads / _batches / _voices) + migration 0029; batches expire after 7 days with an hourly cleanup task, like guest packs. - transcodeToMp3 ffmpeg helper for delivering FX-applied audio as MP3.

Frontend: - /tag-generator page: lead form, five playable voice cards, full FX library (reverb, delay, stutter, pitch-shift, distortion) with presets + sliders, and royalty-free MP3/WAV downloads. - tag-fx engine applies effects entirely in-browser via OfflineAudioContext and encodes WAV client-side; MP3 export is transcoded server-side. - Discoverable CTA added to the marketing landing page.

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