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

scripts/to-yaml.mjs

@@ -0,0 +1,23 @@
+#!/usr/bin/env node
+// Rewrites .archify files from JSON to YAML in place (JSON input is also
+// valid YAML, so already-converted files are simply re-formatted).
+// Usage: node scripts/to-yaml.mjs <file.archify>...
+import fs from 'node:fs';
+import { Document, isSeq, parse, visit } from 'yaml';
+
+export function archifyYaml(value) {
+  const doc = new Document(value);
+  // Short all-scalar lists such as pos/size/viewBox stay on one line.
+  visit(doc, {
+    Seq(_, node) {
+      if (isSeq(node) && node.items.length <= 4 && node.items.every((item) => typeof item.value === 'number')) node.flow = true;
+    },
+  });
+  return doc.toString({ lineWidth: 0, flowCollectionPadding: false });
+}
+
+for (const file of process.argv.slice(2)) {
+  const value = parse(fs.readFileSync(file, 'utf8'));
+  fs.writeFileSync(file, archifyYaml(value));
+  console.log(`yaml: ${file}`);
+}