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>

container/runtime/runtime.ts

@@ -0,0 +1,15 @@
+// Stub: page-side runtime (design §11).
+// Loads layout.json, instantiates widgets in iframes on the 12-column grid,
+// handles edit mode, persists changes via the shell bridge.
+
+declare global {
+  interface Window {
+    __dashShell__?: {
+      call(method: string, args?: unknown): Promise<unknown>;
+    };
+  }
+}
+
+console.info('[dashward-runtime] P0 stub loaded');
+
+export {};