Make HTTP port configurable via HTTP_PORT environment variable (#72)

The HTTPS port was already configurable via HTTPS_PORT, but the HTTP
port was hardcoded to 80. This made it impossible to run multiple
Canasta instances on the same machine without port conflicts.

This change makes HTTP_PORT configurable in .env (defaulting to 80),
matching the existing pattern for HTTPS_PORT. This allows users to run
multiple Canasta instances on the same machine by using different port
combinations (e.g., 8080/8443 for a second instance).

Author: cicalese

.env.example

@@ -1,3 +1,4 @@
+HTTP_PORT=80
 HTTPS_PORT=443
 MYSQL_PASSWORD=mediawiki
 MW_SITE_SERVER=https://localhost

docker-compose.override.yml

@@ -11,6 +11,6 @@ services:
   #elasticsearch:
   caddy:
       ports:
-      - "80:80"
+      - "${HTTP_PORT:-80}:80"
       - "${HTTPS_PORT:-443}:443"
   #varnish: