feat(observer): M-Obs 4-7 — widgets, dashboard, docs, integration example

M-Obs 4: @shade/widgets React library
- ShadeProvider context with observer URL + token + theme
- useShadeState (polling) + useShadeEvents (SSE) hooks
- 7 widgets: IdentityCard, SessionList, PrekeyStock, RecentActivity,
  ServerStatus, FingerprintCompare, WidgetCatalog (meta-widget for
  user-selectable layout with localStorage persistence)
- Self-contained CSS via inline styles, no external CSS conflicts
- Light/dark/auto theme via tokens

M-Obs 5: @shade/dashboard standalone SPA
- Vite + React app composing all widgets into a full debugger layout
- Login screen with token persistence to localStorage
- Build script copies dist/ to @shade/observer/dist/ for embedded serving
- 211 KB JS bundle (66 KB gzipped)

M-Obs 6: Documentation + integration example
- READMEs for @shade/observer and @shade/widgets
- examples/06-observer-dashboard runnable demo: spins up prekey server +
  observer, runs Alice ↔ Bob conversation loop, dashboard at :3901
- Updated root README and docker-compose.yml with observer integration

M-Obs 7: End-to-end verification
- StateAggregator now drains buffered events on subscription, so
  identity.initialized fires before observer construction are still seen
- Verified live: snapshot endpoint returns full state, dashboard serves,
  401 without auth, sessions/messages/ratchet steps all tracked

220 tests passing, 0 failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shade-dashboard/scripts/copy-to-observer.ts

@@ -0,0 +1,26 @@
+/**
+ * After Vite builds the dashboard, copy the dist/ output into
+ * @shade/observer's dist/ directory so the observer endpoint can
+ * serve it from /dashboard/.
+ */
+import { existsSync, mkdirSync, cpSync, rmSync } from 'fs';
+import { join, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+const here = dirname(fileURLToPath(import.meta.url));
+const dashboardDist = join(here, '..', 'dist');
+const observerDist = join(here, '..', '..', 'shade-observer', 'dist');
+
+if (!existsSync(dashboardDist)) {
+  console.error(`Dashboard dist not found at ${dashboardDist}. Run \`vite build\` first.`);
+  process.exit(1);
+}
+
+// Clean and recreate observer dist
+if (existsSync(observerDist)) {
+  rmSync(observerDist, { recursive: true });
+}
+mkdirSync(observerDist, { recursive: true });
+
+cpSync(dashboardDist, observerDist, { recursive: true });
+console.log(`✓ Copied dashboard build to ${observerDist}`);