fix: avoid nginx redirect cycles

[vitormattos]

Summary

• stop recursive internal redirects in the Nginx static-site config
• return 404 for missing assets and sensitive paths like /.env instead of 500
• serve generated HTML files explicitly so pretty URLs such as /account and /pricing keep working

Validation

• docker compose exec web nginx -t
• docker compose exec web nginx -s reload
• curl probes against /account, /pricing, /.env, /robots.txt and /favicon.ico
• verified web logs no longer show "rewrite or internal redirection cycle" after the reload

Notes

• local build_local in this worktree does not currently include a root index.html, so / returns 404 locally after the loop fix; that is separate from the Nginx redirect-cycle bug being fixed here

[github-actions]

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