Registry view with element dialog; Elements and Connectors panels under diagrams

- .archify-registry opens in a new read-only custom editor (archify.registry,
  default): the file's elements as cards; click one for a dialog with its
  description, the defining line (opens the YAML) and the diagrams that use
  it (open on click); Show Source and Open Model work from the view
- the same dialog opens from the registry cards on the model page
- Archify's node index is titled Elements; a Connectors panel built from the
  SVG edges lists from → to with the label, highlights on hover and keeps the
  highlight on click; side by side in the bottom rail
- integration test for the registry view; docs and changelog

src/commands/context.ts

@@ -2,12 +2,14 @@ import * as vscode from 'vscode';
 import { HTML_VIEW_TYPE, HtmlViewerProvider } from '../views/htmlViewer';
 import { ModelService } from '../model/service';
 import { DiagramViewManager } from '../views/diagramView';
+import { RegistryViewProvider } from '../views/registryView';
 
 /** What command handlers share: the extension context and the open views. */
 export interface CommandContext {
   extension: vscode.ExtensionContext;
   views: DiagramViewManager;
   htmlViewer: HtmlViewerProvider;
+  registry: RegistryViewProvider;
   models: ModelService;
 }
 
@@ -18,7 +20,7 @@ export function isHtmlUri(uri: vscode.Uri): boolean {
 /** The file a command applies to: explicit argument, focused preview or viewer, then the text editor. */
 export function targetUri(ctx: CommandContext, arg?: unknown): vscode.Uri | undefined {
   if (arg instanceof vscode.Uri) return arg;
-  return ctx.views.activePreview?.uri ?? ctx.htmlViewer.activeUri ?? vscode.window.activeTextEditor?.document.uri;
+  return ctx.views.activePreview?.uri ?? ctx.registry.activeUri ?? ctx.htmlViewer.activeUri ?? vscode.window.activeTextEditor?.document.uri;
 }
 
 export function sourceUri(ctx: CommandContext, arg?: unknown): vscode.Uri | undefined {