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/0200-containers/web-app.archify

@@ -0,0 +1,38 @@
+schema_version: 1
+diagram_type: architecture
+meta:
+  title: Containers
+  output: containers.html
+components:
+  - ref: user
+    pos: [40, 160]
+    size: [130, 60]
+  - ref: spa
+    pos: [250, 160]
+    size: [150, 60]
+  - ref: api
+    pos: [480, 160]
+    size: [130, 60]
+  - ref: idp
+    pos: [480, 20]
+    size: [130, 60]
+  - ref: cache
+    pos: [690, 60]
+    size: [130, 60]
+  - ref: db
+    pos: [690, 160]
+    size: [130, 60]
+  - ref: storage
+    pos: [690, 260]
+    size: [130, 60]
+boundaries:
+  - kind: region
+    label: Web Application
+    wraps: [spa, api, cache, db, storage]
+connections:
+  - { from: user, to: spa, label: HTTPS, variant: emphasis }
+  - { from: spa, to: api, label: JSON }
+  - { from: api, to: idp, label: verify token, variant: security, labelAt: [531, 110] }
+  - { from: api, to: cache, label: read }
+  - { from: api, to: db, label: SQL }
+  - { from: api, to: storage, label: files }