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

test/integration/suite.ts

@@ -317,6 +317,18 @@ export async function run(): Promise<void> {
     assert.ok(tab);
   });
 
+  await check('a .archify-registry file opens as the registry view and Show Source opens the YAML', async () => {
+    const registry = workspaceFile('model/registry/people.archify-registry');
+    await vscode.commands.executeCommand('vscode.open', registry);
+    const tab = await waitFor('registry view tab', () =>
+      vscode.window.tabGroups.all.flatMap((g) => g.tabs).find((t) => t.isActive && t.input instanceof vscode.TabInputCustom && t.input.viewType === 'archify.registry' && t.input.uri.toString() === registry.toString()),
+    );
+    assert.ok(tab);
+    await vscode.commands.executeCommand('archify.showSource');
+    const editor = await waitFor('registry text editor', () => vscode.window.visibleTextEditors.find((e) => e.document.uri.toString() === registry.toString()));
+    assert.equal(editor.document.languageId, 'yaml');
+  });
+
   await check('Archify | New Diagram… → Model creates main.archify from the folder name', async () => {
     const folder = workspaceFile('new-shop');
     await vscode.workspace.fs.createDirectory(folder);