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/registry/containers.archify-registry

@@ -0,0 +1,40 @@
+schema_version: 1
+elements:
+  ingest:
+    type: backend
+    label: Ingest API
+    sublabel: HTTPS in, events out
+    description: Accepts events from systems that cannot publish to the bus themselves.
+  bus:
+    type: messagebus
+    label: Event bus
+    sublabel: Kafka
+    brand: apache-kafka
+    description: One topic per event type; retained for seven days.
+  router:
+    type: backend
+    label: Event router
+    sublabel: validate, enrich, dispatch
+    description: Checks each event against its schema, adds reference data, hands it to the consumers.
+    diagram: 0300-components/router.archify
+  dlq:
+    type: messagebus
+    label: Dead-letter queue
+    sublabel: failed events
+    description: Events the router could not process; replayed by operations.
+  store:
+    type: database
+    label: Event store
+    sublabel: PostgreSQL
+    brand: postgresql
+    description: Every accepted event, for audit and replay.
+  notifier:
+    type: backend
+    label: Notifier
+    sublabel: email, chat
+    description: Turns selected events into messages to people.
+  analytics:
+    type: database
+    label: Analytics
+    sublabel: warehouse tables
+    description: Flattened events for reporting.