Two coupled changes that let every proxy_pass vhost serve both WS and
SSE without per-vhost flags or template conditionals:
1) nginx.conf: $connection_upgrade map is now always defined (drop
the % if has_websockets: gate), and the '' branch returns "" instead
of "close". With "" + proxy_http_version 1.1, nginx maintains
keep-alive to upstream for non-WS clients — which is what SSE
requires. WS clients still get Connection: upgrade as before.
2) data/nginx/proxy_pass.conf: drop the % if websockets: conditional.
Always set proxy_http_version 1.1 + Upgrade + Connection via the
map, plus proxy_buffering off and proxy_read_timeout 1h for SSE.
Effects on existing vhosts:
- home.server's Proxmox WS vhost: unchanged behavior (the WS branch
was already setting these headers). Gains the ability to also
serve SSE if ever needed.
- All other proxy_pass vhosts (Nextcloud, Freescout, YOURLS, Gitea,
etc.): get keep-alive to upstream (minor latency win) and unbuffered
pass-through (slight throughput cost on huge responses, neutral
for typical web app traffic).
Dead but harmless: bundles/nginx/metadata.py still defaults
nginx/has_websockets to False, and proxmox-ve/grafana still set it
to True. The flag is now a no-op; clean up in a separate pass.
