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-standard-web-app/0300-components/api.archify

@@ -0,0 +1,42 @@
+schema_version: 1
+diagram_type: architecture
+meta:
+  title: API components
+  output: api.html
+components:
+  - ref: spa
+    pos: [40, 160]
+    size: [150, 60]
+  - id: auth
+    type: security
+    label: Auth
+    sublabel: token check
+    pos: [270, 40]
+    size: [130, 60]
+  - id: accounts
+    type: backend
+    label: Accounts
+    pos: [270, 160]
+    size: [130, 60]
+  - id: content
+    type: backend
+    label: Content
+    pos: [270, 280]
+    size: [130, 60]
+  - ref: db
+    pos: [500, 160]
+    size: [130, 60]
+  - ref: storage
+    pos: [500, 280]
+    size: [130, 60]
+boundaries:
+  - kind: region
+    label: API
+    wraps: [auth, accounts, content]
+connections:
+  - { from: spa, to: auth, label: token, variant: security }
+  - { from: spa, to: accounts, label: profile }
+  - { from: spa, to: content, label: pages }
+  - { from: accounts, to: db, label: SQL }
+  - { from: content, to: db, label: SQL }
+  - { from: content, to: storage, label: files }