Fix puzzle-relay crash loop: install pcntl/posix extensions

Workerman requires pcntl and posix on Linux; without them the relay
printed "Please install pcntl extension" and exited immediately,
Docker kept restarting it, and nginx's DNS lookups for
dmtools-puzzle-relay intermittently failed whenever it happened to be
down mid-restart - the "could not be resolved" errors were a symptom
of this crash loop, not a separate networking problem. Local dev never
hit this because Workerman's Windows code path doesn't need either
extension.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker/php/Dockerfile

@@ -6,11 +6,17 @@ RUN apk add --no-cache bash git unzip
 # right system libraries itself, builds, and cleans up - much less fragile
 # than hand-maintaining apk build deps.
 COPY --from=mlocati/php-extension-installer:latest /usr/bin/install-php-extensions /usr/local/bin/
+# pcntl and posix aren't needed by php-fpm itself, but the puzzle-relay
+# service (docker-compose.yml) runs this same image as a Workerman process,
+# and Workerman requires both on Linux (its Windows-only code path, the one
+# used in local dev, doesn't need them - which is why this was missed there).
 RUN install-php-extensions \
     intl \
     pdo_mysql \
     opcache \
-    zip
+    zip \
+    pcntl \
+    posix
 
 COPY --from=composer:2 /usr/bin/composer /usr/bin/composer