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>

src/detect.ts

@@ -13,6 +13,7 @@ export const EVIDENCE_COLLECTIONS: Record<DiagramType, string> = {
 };
 
 const FILENAME_RE = /\.(architecture|workflow|sequence|dataflow|lifecycle)\.json$/i;
+const ARCHIFY_EXT_RE = /\.archify$/i;
 const MAX_SNIFF_BYTES = 8 * 1024 * 1024;
 
 export function isDiagramType(value: unknown): value is DiagramType {
@@ -24,6 +25,22 @@ export function typeFromFilename(fileName: string): DiagramType | undefined {
   return match ? (match[1].toLowerCase() as DiagramType) : undefined;
 }
 
+/** `name.archify`: an Archify diagram whose type comes from `diagram_type`. */
+export function isArchifyFile(fileName: string): boolean {
+  return ARCHIFY_EXT_RE.test(fileName);
+}
+
+/** File names that are diagram sources regardless of their content. */
+export function isDiagramFileName(fileName: string): boolean {
+  return isArchifyFile(fileName) || FILENAME_RE.test(fileName);
+}
+
+/** Base name without the diagram source extension (`web.archify` → `web`). */
+export function diagramBaseName(fileName: string): string {
+  const base = fileName.split(/[\\/]/).pop() ?? fileName;
+  return base.replace(ARCHIFY_EXT_RE, '').replace(/\.json$/i, '');
+}
+
 export interface DiagramSource {
   type: DiagramType;
   diagram: Record<string, unknown>;