tag3: Quadlet-Dateien für VisitCounter freigegeben

- listings/visitcounter/quadlets/ mit 5 Unit-Dateien hinzugefügt
  (app, db, proxy .container + .network + .volume)
- wird in Exercise 18 verwendet

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

listings/visitcounter/quadlets/visitcounter-app.container

@@ -0,0 +1,16 @@
+[Container]
+Image=localhost/visitcounter:latest
+Environment=DB_HOST=systemd-visitcounter-db
+Environment=DB_NAME=visitcount
+Environment=DB_USER=app
+Environment=DB_PASSWORD=secret
+Network=visitcounter-app.network
+
+[Unit]
+After=visitcounter-db.service
+
+[Service]
+Restart=always
+
+[Install]
+WantedBy=default.target

listings/visitcounter/quadlets/visitcounter-app.network

@@ -0,0 +1 @@
+[Network]

listings/visitcounter/quadlets/visitcounter-db.container

@@ -0,0 +1,13 @@
+[Container]
+Image=postgres:16-alpine
+Environment=POSTGRES_DB=visitcount
+Environment=POSTGRES_USER=app
+Environment=POSTGRES_PASSWORD=secret
+Volume=visitcounter-db.volume:/var/lib/postgresql/data
+Network=visitcounter-app.network
+
+[Service]
+Restart=always
+
+[Install]
+WantedBy=default.target

listings/visitcounter/quadlets/visitcounter-db.volume

@@ -0,0 +1 @@
+[Volume]

listings/visitcounter/quadlets/visitcounter-proxy.container

@@ -0,0 +1,14 @@
+[Container]
+Image=nginx:1.27-alpine
+PublishPort=8080:80
+Volume=%h/visitcounter/nginx/default.conf:/etc/nginx/conf.d/default.conf:ro
+Network=visitcounter-app.network
+
+[Unit]
+After=visitcounter-app.service
+
+[Service]
+Restart=always
+
+[Install]
+WantedBy=default.target