feat: initial app template catalog with 16 apps

Populate the appstore-apptemplates repo with catalog.json and
per-app config files for all 16 curated Docker apps, each at v1.0.0.

apps/postgres/app.json

@@ -0,0 +1,10 @@
+{
+  "id": "postgres",
+  "name": "PostgreSQL",
+  "description": "Advanced open-source relational database",
+  "category": "Databases",
+  "iconName": "postgres",
+  "latestVersion": "1.0.0",
+  "versions": ["1.0.0"],
+  "maintainer": "serve.zone"
+}

apps/postgres/versions/1.0.0/config.json

@@ -0,0 +1,18 @@
+{
+  "image": "postgres:16-alpine",
+  "port": 5432,
+  "envVars": [
+    {
+      "name": "POSTGRES_PASSWORD",
+      "required": true
+    },
+    {
+      "name": "POSTGRES_USER",
+      "default": "postgres"
+    },
+    {
+      "name": "POSTGRES_DB",
+      "default": "postgres"
+    }
+  ]
+}