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/styles.css

@@ -0,0 +1,22 @@
+:root {
+  --bg: #f5f5f7;
+  --fg: #1c1c1e;
+  --grid-gap: 16px;
+}
+
+[data-theme="dark"] {
+  --bg: #0f0f12;
+  --fg: #f0f0f5;
+}
+
+html, body { margin: 0; padding: 0; height: 100%; background: var(--bg); color: var(--fg); }
+body { font-family: ui-sans-serif, system-ui, -apple-system, sans-serif; }
+
+#grid {
+  display: grid;
+  grid-template-columns: repeat(12, 1fr);
+  gap: var(--grid-gap);
+  padding: var(--grid-gap);
+  min-height: 100%;
+  box-sizing: border-box;
+}