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-event-based-integration/0200-containers/platform.archify

@@ -0,0 +1,46 @@
+schema_version: 1
+diagram_type: architecture
+meta:
+  title: Containers
+  output: containers.html
+components:
+  - ref: crm
+    pos: [40, 60]
+    size: [130, 60]
+  - ref: erp
+    pos: [40, 260]
+    size: [130, 60]
+  - ref: ingest
+    pos: [250, 160]
+    size: [140, 60]
+  - ref: bus
+    pos: [470, 160]
+    size: [140, 60]
+  - ref: router
+    pos: [690, 160]
+    size: [150, 60]
+  - ref: dlq
+    pos: [690, 320]
+    size: [150, 60]
+  - ref: store
+    pos: [920, 60]
+    size: [140, 60]
+  - ref: notifier
+    pos: [920, 160]
+    size: [140, 60]
+  - ref: analytics
+    pos: [920, 260]
+    size: [140, 60]
+boundaries:
+  - kind: region
+    label: Integration platform
+    wraps: [ingest, bus, router, dlq, store, notifier, analytics]
+connections:
+  - { from: crm, to: ingest, label: HTTPS, variant: emphasis }
+  - { from: erp, to: ingest, label: HTTPS, variant: emphasis }
+  - { from: ingest, to: bus, label: publish }
+  - { from: bus, to: router, label: consume }
+  - { from: router, to: store, label: append }
+  - { from: router, to: notifier, label: notify }
+  - { from: router, to: analytics, label: flatten }
+  - { from: router, to: dlq, label: failed, variant: dashed, labelDy: 24 }