Support .archify diagram files (0.2.0)

.archify files are Archify JSON diagram sources. They open as JSON,
preview with the same commands, report validation problems, and get
completion from a schema that dispatches on diagram_type. Adds a
hello.archify example and tests for detection, the dispatching schema
and the VS Code behaviour.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -1,18 +1,19 @@
 {
   "name": "archify-vscode-ext",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "archify-vscode-ext",
-      "version": "0.1.0",
+      "version": "0.2.0",
       "license": "MIT",
       "devDependencies": {
         "@types/node": "^22.0.0",
         "@types/vscode": "~1.100.0",
         "@vscode/test-electron": "^3.1.0",
         "@vscode/vsce": "^3.0.0",
+        "ajv": "^8.20.0",
         "esbuild": "^0.25.0",
         "jsonc-parser": "^3.3.1",
         "typescript": "^5.8.0"