build: add self-hosted Fleet deployment

[SamuelPalubaCZ]

Related issue: N/A

Checklist for submitter

• Timeouts are implemented and retries are limited to avoid infinite loops

Testing

• QA'd all new/changed functionality manually
• Built Fleet locally from source at commit b0223221a4
• Validated docker compose config and the Caddy configuration
• Verified Fleet, MySQL, Redis, and Caddy containers
• Verified frontend bundle and initial setup/login through public HTTPS
• Verified https://fleet.thinkhome.org/healthz through public DNS, OPNsense NAT, and trusted HTTPS
• Deployed and verified the env-driven Compose configuration

Deployment notes

• Secrets stay in ignored .env; .env.example contains placeholders only.
• .env is excluded from the Docker build context and cache.
• Fleet port 1337 is internal to the Compose network.
• Caddy publishes TCP 80/443 and terminates TLS.
• Fleet trusts one reverse-proxy hop for the client IP.