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-widgets/src/index.ts

@@ -0,0 +1,18 @@
+export { ShadeProvider, useShadeContext } from './ShadeProvider.js';
+export { useShadeState } from './useShadeState.js';
+export { useShadeEvents } from './useShadeEvents.js';
+export { darkTheme, lightTheme, resolveTheme } from './theme.js';
+
+export { IdentityCard } from './components/IdentityCard.js';
+export { SessionList } from './components/SessionList.js';
+export { PrekeyStock } from './components/PrekeyStock.js';
+export { RecentActivity } from './components/RecentActivity.js';
+export { ServerStatus } from './components/ServerStatus.js';
+export { FingerprintCompare } from './components/FingerprintCompare.js';
+export { WidgetCatalog } from './components/WidgetCatalog.js';
+
+export type { ShadeProviderProps, ShadeContextValue } from './ShadeProvider.js';
+export type { ShadeState, UseShadeStateResult } from './useShadeState.js';
+export type { ShadeEventEnvelope, UseShadeEventsResult } from './useShadeEvents.js';
+export type { ShadeTheme, ThemeMode } from './theme.js';
+export type { WidgetCatalogProps, WidgetKey } from './components/WidgetCatalog.js';