Release v0.5.0

[do0ori]

Summary

• add reliable timer completion alerts with Web Push and a Cloudflare Durable Object scheduler when the PWA is backgrounded
• register the Vite development service worker with its app-shell fallback, and retain an actionable registration failure diagnostic
• subscribe after notification permission was granted outside the background-alert flow, so completion Push alerts are still scheduled
• show a single running-status notification and provide a Test alert control in Timer & Sound settings
• persist custom uploaded alarm audio, make previews controllable, and allow removal from settings
• enable Cloudflare Worker observability and tighten About & Developer setting-item spacing
• add explicit Background alerts settings, local Worker API configuration, deployment configuration, and v0.5.0 release metadata

Verification

• npm test (13 suites, 30 tests)
• manually verified local service-worker registration and Test alert notification
• manually verified local completion Web Push delivery from the deployed Cloudflare Worker
• npx wrangler deploy