fix(deploy): put landing on proxy's network + runtime DNS resolve

The landing service had no networks: key, so it joined the auto 'default'
network while proxy was only on spaceshell-network + webproxy — they shared no
network, so proxy_pass to 'landing' couldn't resolve. With a static
upstream{ server landing:80 } nginx fails to boot on an unresolvable name and
restart-loops, so the proxy flapped (page intermittently up/down). Fixes:
- landing now joins spaceshell-network (shared with proxy).
- proxy.conf resolves 'landing' at request time via Docker DNS (127.0.0.11)
  using a variable proxy_pass, so nginx starts even if landing is briefly down.
nginx -t passes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

deploy/docker-compose.yaml

@@ -8,6 +8,9 @@ services:
     restart: unless-stopped
     expose:
       - "80"
+    networks:
+      # Must share a network with `proxy`, else proxy_pass to `landing` can't resolve.
+      - spaceshell-network
 
   proxy:
     image: nginx:1.27-alpine

deploy/proxy.conf

@@ -1,14 +1,16 @@
 # Front nginx for spaceshell.ru — reverse-proxies the landing container and
 # serves macOS .dmg downloads from the host-mounted ./download volume.
-upstream landing_upstream {
-    server landing:80;
-}
-
 server {
     listen 80;
     listen [::]:80;
     server_name spaceshell.ru www.spaceshell.ru;
 
+    # Resolve `landing` at request time via Docker's embedded DNS, so nginx
+    # starts even if the landing container is momentarily down (a static
+    # `upstream { server landing:80; }` makes nginx fail to boot when the name
+    # can't be resolved, restart-looping the proxy → flapping page).
+    resolver 127.0.0.11 valid=10s ipv6=off;
+
     # Stable download URL: /download/spacesh.dmg → ./download/spacesh.dmg on host.
     location /download/ {
         alias /srv/download/;
@@ -21,7 +23,9 @@ server {
     }
 
     location / {
-        proxy_pass http://landing_upstream;
+        # Variable in proxy_pass forces runtime resolution (with the resolver above).
+        set $landing http://landing:80;
+        proxy_pass $landing;
         proxy_set_header Host              $host;
         proxy_set_header X-Real-IP         $remote_addr;
         proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;