chore: P0 skeleton

Bootstrap the Dashward repo per arch/UBUNTU-DASHBOARD-SPACE.md:

- pnpm-workspaces monorepo (sdk, extension, container, widgets-builtin/*)
- GNOME extension stub (metadata.json, src/*.ts placeholders for warden,
  guard, supervisor, entry UX, DBus service)
- WebKit container stub (GJS main + page-side runtime + dashboard.html)
- TypeScript widget SDK (defineWidget + types)
- Builtin clock widget as the first SDK consumer example
- DBus interface XML (proto/shell.iface.xml) and shared types
- esbuild configs for extension and container; tsc for SDK
- Design doc copied in at repo root for discoverability

No functional logic yet -- all components are placeholders that compose
in extension.ts so the build chain can be exercised. P1 (workspace
warden) starts next.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

extension/esbuild.config.js

@@ -0,0 +1,28 @@
+import esbuild from 'esbuild';
+
+const watch = process.argv.includes('--watch');
+
+const opts = {
+  entryPoints: ['src/extension.ts'],
+  bundle: true,
+  outfile: 'dist/extension.js',
+  format: 'esm',
+  target: 'firefox128',
+  platform: 'neutral',
+  external: [
+    'gi://*',
+    'resource:///*',
+    'system',
+    'cairo',
+    'gettext',
+  ],
+  sourcemap: 'inline',
+  logLevel: 'info',
+};
+
+if (watch) {
+  const ctx = await esbuild.context(opts);
+  await ctx.watch();
+} else {
+  await esbuild.build(opts);
+}