0.3.0: .archify files are YAML and open straight into the diagram

- .archify content is YAML (JSON still accepted); converted to JSON for the renderer
- Archify Diagram custom editor is the default for *.archify; Show Source opens the YAML beside it
- YAML syntax errors and validation problems mapped to YAML lines
- yamlValidation for schema completion with redhat.vscode-yaml
- scripts/to-yaml.mjs converts existing .archify files

examples/hello.archify

@@ -1,17 +1,28 @@
-{
-  "schema_version": 1,
-  "diagram_type": "architecture",
-  "meta": {
-    "title": "Hello Archify",
-    "output": "hello.html"
-  },
-  "components": [
-    { "id": "browser", "type": "frontend", "label": "Browser", "pos": [40, 120], "size": [140, 60] },
-    { "id": "api", "type": "backend", "label": "API", "pos": [260, 120], "size": [140, 60] },
-    { "id": "db", "type": "database", "label": "PostgreSQL", "pos": [480, 120], "size": [140, 60] }
-  ],
-  "connections": [
-    { "from": "browser", "to": "api", "label": "HTTPS" },
-    { "from": "api", "to": "db", "label": "SQL" }
-  ]
-}
+schema_version: 1
+diagram_type: architecture
+meta:
+  title: Hello Archify
+  output: hello.html
+components:
+  - id: browser
+    type: frontend
+    label: Browser
+    pos: [40, 120]
+    size: [140, 60]
+  - id: api
+    type: backend
+    label: API
+    pos: [260, 120]
+    size: [140, 60]
+  - id: db
+    type: database
+    label: PostgreSQL
+    pos: [480, 120]
+    size: [140, 60]
+connections:
+  - from: browser
+    to: api
+    label: HTTPS
+  - from: api
+    to: db
+    label: SQL