Add a 3D view of every diagram; organise source by job; 0.6.0

3D view: a "3D" menu beside Export switches the diagram to a three.js
scene built from the live Archify SVG. Nodes become blocks topped with
the node as Archify draws it, relationships become lit pipes along
Archify's routes, and the canvas, frames, lanes and legend form the
floor. Clicks and hover go to the SVG nodes, so focus, the Semantic
Passport and the intent trace work as in 2D; Archify's own animations
(trace, node pulse, passport/path/lens flows) are mirrored live. The
menu also offers flat or stacked levels, reset view and a top view;
Export gains "3D view" (PNG). Trackpad scrolling pans, pinch and the
mouse wheel zoom, and the zoom buttons work beyond the 2D limits.
The scene draws only when something moves. New setting
archify.defaultView.

Source: src/ is split by job (commands, views, webview, archify,
sources, language, util, viewer3d); behaviour unchanged.

src/commands/context.ts

@@ -0,0 +1,38 @@
+import * as vscode from 'vscode';
+import { HTML_VIEW_TYPE, HtmlViewerProvider } from '../views/htmlViewer';
+import { DiagramViewManager } from '../views/diagramView';
+
+/** What command handlers share: the extension context and the open views. */
+export interface CommandContext {
+  extension: vscode.ExtensionContext;
+  views: DiagramViewManager;
+  htmlViewer: HtmlViewerProvider;
+}
+
+export function isHtmlUri(uri: vscode.Uri): boolean {
+  return /\.html?$/i.test(uri.path);
+}
+
+/** 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;
+}
+
+export function sourceUri(ctx: CommandContext, arg?: unknown): vscode.Uri | undefined {
+  const uri = targetUri(ctx, arg);
+  if (!uri) vscode.window.showWarningMessage('Archify: open a .archify diagram first.');
+  return uri;
+}
+
+export const openHtmlViewer = (uri: vscode.Uri, viewColumn?: vscode.ViewColumn) =>
+  vscode.commands.executeCommand('vscode.openWith', uri, HTML_VIEW_TYPE, viewColumn);
+
+export async function exists(uri: vscode.Uri): Promise<boolean> {
+  try {
+    await vscode.workspace.fs.stat(uri);
+    return true;
+  } catch {
+    return false;
+  }
+}