feat: add OpenSourcePOS template

[BinkyTwin]

Summary

• add an OpenSourcePOS template backed by the upstream jekkos/opensourcepos:master Docker image
• configure Dokploy domain routing, MariaDB persistence, generated database credentials, upload/log volumes, and allowed hostnames
• add README mount, SVG logo, and metadata entry

/claim #152
Closes #860

Validation

• node dedupe-and-sort-meta.js
• node --import ./build-scripts/node_modules/tsx/dist/loader.mjs build-scripts/validate-template.ts --dir blueprints/opensourcepos
• node --import ./build-scripts/node_modules/tsx/dist/loader.mjs build-scripts/validate-docker-compose.ts --file blueprints/opensourcepos/docker-compose.yml
• MYSQL_ROOT_PASSWORD=root-password MYSQL_DATABASE=ospos MYSQL_USER=admin MYSQL_PASSWORD=app-password PHP_TIMEZONE=UTC FORCE_HTTPS=false ALLOWED_HOSTNAMES=pos.example.com docker compose -f blueprints/opensourcepos/docker-compose.yml config
• git diff --check
• Docker Hub API confirmed jekkos/opensourcepos:master is available for amd64 and arm64

Note: upstream docker-compose.yml currently uses jekkos/opensourcepos:master; the latest GitHub release tag exists, but the matching Docker tag is amd64-only, so this template follows upstream while preserving Apple Silicon/server ARM compatibility.

[github-actions]

built with Refined Cloudflare Pages Action

⚡ Cloudflare Pages Deployment

Name	Status	Preview	Last Commit
templates	✅ Ready (View Log)	Visit Preview	cc281ec

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.