revert: remove ringing audio feature and clean up oscillators

fix(dialogue): make rating classification robust to phonetic transcribing errors and fix missing variable references

feat(frontend): add synthesizer for telephone ringing audio via Web Audio API

fix(frontend): clear overlapping ringing timers to prevent false call ended states

fix(vite): configure relative base path for static hosting compatibility

feat: add automatic local/production backend URL routing and ignore zip files

fix(config): default port to 7860 to match Hugging Face Space app_port configuration

fix(database): allow executing multiple SQL statements in SQLite via executescript

feat: add local SQLite database fallback for zero-config deployments

docs: add YAML metadata config header for Hugging Face Space

feat: deploy production voice agent with automated multi-call scheduling