Ship the three C4 examples and model:scaffold --example

- examples/: c4-standard-web-app, c4-e-shop (was online-shop),
  c4-event-based-integration; the same models the extension offers
  under Archify | New Model…
- model-scaffold --example <name> copies one and renames id, name,
  description and the overview title; never overwrites
- tests cover every example and the copy; docs updated

examples/c4-event-based-integration/0100-context/platform.archify

@@ -0,0 +1,26 @@
+schema_version: 1
+diagram_type: architecture
+meta:
+  title: System context
+  output: context.html
+components:
+  - ref: crm
+    pos: [40, 60]
+    size: [130, 60]
+  - ref: erp
+    pos: [40, 260]
+    size: [130, 60]
+  - ref: platform
+    pos: [280, 160]
+    size: [170, 60]
+  - ref: warehouse
+    pos: [540, 60]
+    size: [150, 60]
+  - ref: ops
+    pos: [540, 260]
+    size: [150, 60]
+connections:
+  - { from: crm, to: platform, label: customer events, variant: emphasis }
+  - { from: erp, to: platform, label: order events, variant: emphasis }
+  - { from: platform, to: warehouse, label: pick lists }
+  - { from: ops, to: platform, label: replays, variant: dashed }