Add unavailable page when PHP-FPM is down: Caddy handle_errors on 502/503

- Create unavailable.html static page with neo-brutalist design and retry button
- Add handle_errors in Caddy for 502/503: serve unavailable.html
- Add dial/read/write timeouts to php_fastcgi (5s/30s/30s)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ansible/caddy.j2

@@ -3,7 +3,7 @@ ticket.e-cosplay.fr {
         dns cloudflare {{ cloudflare_api_token }}
     }
 
-    @static path /logo.png /favicon.ico /favicon.png /marker.png /screen.png /manifest.json /site.webmanifest /sw.js /workbox/* /idb/* /build/* /uploads/* /pwa/*
+    @static path /logo.png /favicon.ico /favicon.png /marker.png /screen.png /manifest.json /site.webmanifest /sw.js /unavailable.html /workbox/* /idb/* /build/* /uploads/* /pwa/*
     handle @static {
         root * /var/www/e-ticket/public
         file_server
@@ -38,11 +38,23 @@ ticket.e-cosplay.fr {
             root /app/public
             lb_policy round_robin
             trusted_proxies private_ranges
+            dial_timeout 5s
+            read_timeout 30s
+            write_timeout 30s
         }
         file_server
         try_files {path} /index.php?{query}
     }
 
+    handle_errors {
+        @unavailable expression `{err.status_code} in [502, 503]`
+        handle @unavailable {
+            root * /var/www/e-ticket/public
+            rewrite * /unavailable.html
+            file_server
+        }
+    }
+
     encode gzip
 
     header {