Suggest brand IDs after brand: and place unknown-brand errors on their line

- Completion for brand values in .archify (YAML) and Archify JSON sources,
  from the bundled brand-marks/catalog.json (107 marks); aliases and
  product names match, so "kafka" offers apache-kafka
- brand/unknown diagnostics carry their JSON pointer only at the start of
  the message; use it when subject.path is missing, so the error lands on
  the brand line instead of the top of the file
- Unit tests for catalog loading, value detection and pointer fallback;
  integration checks for completion and diagnostic placement

Closes #5

src/extension.ts

@@ -1,6 +1,7 @@
 import fs from 'node:fs/promises';
 import path from 'node:path';
 import * as vscode from 'vscode';
+import { BRAND_COMPLETION_SELECTOR, BrandCompletionProvider } from './brandCompletion';
 import { diagramBaseName, isArchifyFile, isArchifyHtml, isDiagramFileName, readDiagramSource } from './detect';
 import { DiagnosticsController } from './diagnostics';
 import { HTML_VIEW_TYPE, HtmlViewerProvider } from './htmlViewer';
@@ -18,7 +19,13 @@ function isHtmlUri(uri: vscode.Uri): boolean {
 export function activate(context: vscode.ExtensionContext): void {
   const previews = new PreviewManager(context);
   const htmlViewer = new HtmlViewerProvider();
-  context.subscriptions.push(previews, htmlViewer, new DiagnosticsController(context), log());
+  context.subscriptions.push(
+    previews,
+    htmlViewer,
+    new DiagnosticsController(context),
+    log(),
+    vscode.languages.registerCompletionItemProvider(BRAND_COMPLETION_SELECTOR, new BrandCompletionProvider(context.extensionPath), ' ', '"'),
+  );
 
   /** The file a command applies to: explicit argument, focused preview or viewer, then the text editor. */
   function targetUri(arg?: unknown): vscode.Uri | undefined {