Add Archify | New Model… with three C4 examples and Open Model in the Explorer menu

- templates/models: C4 - Standard Web App, C4 - E-Shop, C4 - Event-Based
  Integration; each a complete model (main.archify, registry, context,
  containers, components) that validates
- archify.newModel: pick an example and a folder name, copy it, name the
  model after the folder, open the model page
- Explorer menu: New Model… on folders, Open Model on .archify and
  .archify-registry files; File → New File… lists New Model…
- unit test validates every example end to end; integration test runs the
  command; README, CHANGELOG, docs/model.md

templates/models/c4-e-shop/registry/containers.archify-registry

@@ -0,0 +1,37 @@
+schema_version: 1
+elements:
+  web:
+    type: frontend
+    label: Web App
+    sublabel: React
+    brand: react
+    description: The shop as customers see it; talks only to the API.
+  api:
+    type: backend
+    label: API
+    sublabel: Node.js
+    brand: node-js
+    description: Owns authentication, orders and the catalogue.
+    diagram: 0300-components/api.archify
+  worker:
+    type: backend
+    label: Worker
+    sublabel: async jobs
+    description: Picks jobs from the queue; emails, invoices, exports.
+  queue:
+    type: messagebus
+    label: Queue
+    sublabel: SQS
+    description: Job queue between the API and the workers.
+  db:
+    type: database
+    label: Database
+    sublabel: PostgreSQL
+    brand: postgresql
+    description: Orders, customers and catalogue; the source of truth.
+  cache:
+    type: database
+    label: Cache
+    sublabel: Redis
+    brand: redis
+    description: Sessions and catalogue cache; nothing here is the source of truth.