Health check endpoint returns 400 for HTTP/1.0 requests without Host header

## Description The `/health` endpoint returns HTTP 400 Bad Request when accessed by load balancer health checks that use HTTP/1.0 without a `Host` header. ## Environment - Image: `zulip/docker-zulip:9.3-0` - Configuration: `DISABLE_HTTPS: "True"` with `LOADBALANCER_IPS` configured ## Steps to Reproduce 1. Configure Zulip behind a load balancer with TLS termination 2. Configure LB health check to probe `/health` endpoint 3. LB sends HTTP/1.0 request without Host header (common for many cloud LB health probes) ## Observed Behavior ``` 10.0.0.3 - - [22/Jan/2026:17:02:08 +0000] "GET /health HTTP/1.0" 400 143 "-" "-" 0.002 ``` The request returns 400 Bad Request. ## Expected Behavior The `/health` endpoint should return 200 OK for health check requests, even without a `Host` header, since: 1. Many cloud load balancers (AWS ALB/NLB, GCP, Azure LB) use HTTP/1.0 for health probes 2. HTTP/1.0 does not require a Host header 3. The `/health` endpoint is specifically designed for load balancer health checks ## Workaround Configure the load balancer to send a `Host` header with the health check request. ## Suggested Fix Add a `server` block in nginx that handles requests without a `Host` header for the `/health` endpoint, similar to: ```nginx server { listen 80 default_server; server_name ""; location = /health { proxy_pass http://127.0.0.1:9993/api/v1/server_settings; # or return the health check response directly } location / { return 400; } } ``` Or configure the existing health check location to work in the default server block.