feat: add autoplay countdown

[Priveetee]

Summary

• add a 10-second autoplay countdown overlay after a watched video ends
• show the next video thumbnail, title, channel, progress bar, play-now action, pause/resume control, and cancel action
• stabilize Vidstack progress and seek persistence events around ended playback
• update frontend dependencies, Biome, and audit overrides
• patch frontend image Alpine packages while keeping nginx root and port 80 for runtime compatibility
• keep the existing dev branch performance and issue-template updates ready for main

Production behavior

• autoplay still navigates only to the resolved next playlist video
• canceling the overlay stops only the current autoplay countdown
• no backend API changes are required
• the frontend container keeps the existing internal port 80 contract
• refs [Feature Request] Add delay to autoplay #110

Verification

• bun run --cwd apps/web tsc -b --force
• bun run check
• bun audit
• bun run build
• docker compose -f docker-compose.yml config --quiet
• docker compose -f docker-compose.dev.yml config --quiet
• docker build --load -t typetype-frontend-security-check .
• trivy image scan for HIGH and CRITICAL fixed vulnerabilities
• git diff --check

Rollback

• revert the autoplay overlay and ended-navigation commits if playback ending regresses
• revert the progress event stabilization commit if progress persistence regresses
• revert the dependency and Docker package commits if the production image build regresses