build(web): switch to alpine-based nginx runner for sub_filter support

Migrate the web runner stage from the official nginx alpine image to a
standard alpine image with the nginx package installed. This ensures
the presence of the `http_sub_module` required for path rewriting in
the telemetry proxy configuration.

- Replace `nginx:1.27-alpine` with `alpine:3.20` and `apk add nginx`
- Update Nginx configuration file path to `/etc/nginx/http.d/default.conf`
- Update web asset root directory to `/var/lib/nginx/html`
- Add `X-Forwarded-For` and `X-Forwarded-Proto` headers to proxy locations

apps/web/nginx.conf

@@ -1,7 +1,7 @@
 server {
   listen 80;
   server_name _;
-  root /usr/share/nginx/html;
+  root /var/lib/nginx/html;
   index index.html;
 
   location /api/ {
@@ -28,6 +28,8 @@ server {
     proxy_http_version 1.1;
     proxy_set_header Host $host;
     proxy_set_header X-Real-IP $remote_addr;
+    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+    proxy_set_header X-Forwarded-Proto $scheme;
     expires 1y;
     add_header Cache-Control "public, immutable";
   }
@@ -57,7 +59,7 @@ server {
     proxy_read_timeout 10s;
   }
 
-  # Telemetry SPA — proxy to orange, rewrite root-relative paths to prefix
+  # Telemetry SPA — proxy to orange VPS, rewrite root-relative paths to /telemetry/ prefix
   location /telemetry/ {
     proxy_pass http://100.96.248.86:8181/;
     proxy_http_version 1.1;
@@ -69,7 +71,7 @@ server {
     proxy_send_timeout 35s;
     proxy_read_timeout 35s;
 
-    # Rewrite root-relative paths in HTML/JS to /telemetry/ prefix
+    # Rewrite root-relative paths (<script src="/", href="/", fetch("/")) to /telemetry/ prefix
     sub_filter_types text/html application/javascript;
     sub_filter_once off;
     sub_filter 'src="/' 'src="/telemetry/';