Add New Diagram command with starter templates

- Archify: New Diagram… (Explorer folder menu, File > New File…, Command
  Palette) creates a .archify file from a template and opens the diagram
- Six YAML templates: architecture, workflow, sequence, dataflow,
  lifecycle and an everyday plan; connections carry ids, workflows use
  schema 2
- Title and meta.output follow the file name; template comments are kept
- Tests: every template passes archify validate; integration check for
  the command

Closes #2

templates/lifecycle.archify

@@ -0,0 +1,53 @@
+# Lifecycle: the states something moves through and what moves it.
+# States sit in lanes and columns; transitions link state ids.
+schema_version: 1
+diagram_type: lifecycle
+meta:
+  title: Order Status
+  output: lifecycle.html
+  viewBox: [880, 566]
+lanes:
+  - id: main
+    label: Normal path
+  - id: exits
+    label: Exits
+states:
+  - id: placed
+    type: start
+    label: Placed
+    lane: main
+    col: 0
+  - id: paid
+    type: active
+    label: Paid
+    lane: main
+    col: 1
+  - id: shipped
+    type: active
+    label: Shipped
+    lane: main
+    col: 2
+  - id: delivered
+    type: success
+    label: Delivered
+    lane: main
+    col: 3
+  - id: cancelled
+    type: failure
+    label: Cancelled
+    lane: exits
+    col: 0
+transitions:
+  - id: pay
+    from: placed
+    to: paid
+  - id: ship
+    from: paid
+    to: shipped
+  - id: deliver
+    from: shipped
+    to: delivered
+  - id: cancel
+    from: placed
+    to: cancelled
+    variant: security