fix: resolver-based nginx config and env vars for template configs

- Use Docker embedded DNS (127.0.0.11) with variables in proxy_pass
  instead of upstream blocks to prevent nginx crash loops when
  backend isn't ready during startup
- Add STACK_NAME env to web and livekit services for golang
  template_driver config resolution
- Add LIVEKIT_API_KEY env to livekit service for config template
- Add livekit_as secret to livekit service
- Increase web healthcheck retries and start_period
- Bump NGINX_CONF_VERSION to v2

nginx.conf.tmpl

@@ -1,10 +1,7 @@
-upstream meet_backend {
-    server {{ env "STACK_NAME" }}_backend:8000 fail_timeout=0;
-}
-
-upstream meet_frontend {
-    server {{ env "STACK_NAME" }}_app:8080 fail_timeout=0;
-}
+# Use Docker's embedded DNS so nginx starts even if upstreams aren't ready yet.
+# With variables in proxy_pass, hostname resolution is deferred to request time
+# instead of config parse time — preventing crash loops during slow backend startup.
+resolver 127.0.0.11 valid=5s;
 
 server {
     listen 8083;
@@ -14,13 +11,16 @@ server {
     # Disables server version feedback on pages and in headers
     server_tokens off;
 
+    set $meet_backend {{ env "STACK_NAME" }}_backend:8000;
+    set $meet_frontend {{ env "STACK_NAME" }}_app:8080;
+
     location @proxy_to_meet_backend {
         proxy_set_header X-Forwarded-Proto https;
         proxy_set_header Host $http_host;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 
         proxy_redirect off;
-        proxy_pass http://meet_backend;
+        proxy_pass http://$meet_backend;
     }
 
     location @proxy_to_meet_frontend {
@@ -29,7 +29,7 @@ server {
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 
         proxy_redirect off;
-        proxy_pass http://meet_frontend;
+        proxy_pass http://$meet_frontend;
     }
 
     location / {