Wire all integrations + production hardening: 15 recommendations

Integration & Wiring:
- useStore/useAppState wired into App.tsx (replaces 8 useState calls)
- React Router wired at app root (URL-based navigation)
- SparklineChart/MetricCard/BarChart integrated into Admin + Ethics pages
- useNotifications.handleWSEvent wired into WebSocket handler
- Notification center dropdown in header with unread badge
- Locale selector added to Settings page (6 languages)
- Dashboard data fetching with 10s polling into MetricCards
- File drag-and-drop support on chat area

Production Hardening:
- PostgresStateBackend with connection pooling (psycopg2)
- App lifespan wires backend from FUSIONAGI_DB_BACKEND env (memory|sqlite|postgres)
- Redis cache wired from FUSIONAGI_REDIS_URL env at startup
- Multi-process uvicorn config for horizontal scaling

Testing:
- Playwright visual regression tests (12 stories x 2 viewports)
- k6 load test script with ramp/spike/ramp-down stages
- 7 new Python tests (postgres fallback, app wiring)

575 Python tests + 45 frontend tests = 620 total, 0 ruff errors.

Co-Authored-By: Nakamoto, S <defi@defi-oracle.io>

frontend/e2e/visual.config.ts

@@ -0,0 +1,33 @@
+/**
+ * Visual regression testing with Playwright screenshots.
+ *
+ * Run: npx playwright test --config=e2e/visual.config.ts
+ */
+
+import { defineConfig, devices } from '@playwright/test'
+
+export default defineConfig({
+  testDir: '.',
+  testMatch: 'visual.spec.ts',
+  timeout: 30000,
+  expect: {
+    toHaveScreenshot: {
+      maxDiffPixelRatio: 0.05,
+      threshold: 0.2,
+    },
+  },
+  use: {
+    baseURL: 'http://localhost:6006', // Storybook
+    screenshot: 'on',
+  },
+  projects: [
+    { name: 'desktop', use: { ...devices['Desktop Chrome'] } },
+    { name: 'mobile', use: { ...devices['iPhone 13'] } },
+  ],
+  webServer: {
+    command: 'npx storybook dev -p 6006 --no-open',
+    port: 6006,
+    reuseExistingServer: true,
+    timeout: 60000,
+  },
+})

frontend/e2e/visual.spec.ts

@@ -0,0 +1,31 @@
+/**
+ * Visual regression tests against Storybook stories.
+ *
+ * Run: npx playwright test --config=e2e/visual.config.ts
+ * First run creates baseline screenshots; subsequent runs compare.
+ */
+
+import { test, expect } from '@playwright/test'
+
+const STORIES = [
+  { name: 'Avatar', path: '/iframe.html?id=components-avatar--default' },
+  { name: 'ChatMessage-User', path: '/iframe.html?id=components-chatmessage--user-message' },
+  { name: 'ChatMessage-Assistant', path: '/iframe.html?id=components-chatmessage--assistant-message' },
+  { name: 'ChatMessage-Code', path: '/iframe.html?id=components-chatmessage--with-code-block' },
+  { name: 'Markdown-Basic', path: '/iframe.html?id=components-markdown--basic-text' },
+  { name: 'Markdown-Code', path: '/iframe.html?id=components-markdown--code-block' },
+  { name: 'Skeleton-Single', path: '/iframe.html?id=components-skeleton--single-line' },
+  { name: 'Skeleton-Multi', path: '/iframe.html?id=components-skeleton--multiple-lines' },
+  { name: 'Toast-Info', path: '/iframe.html?id=components-toast--info' },
+  { name: 'Toast-Error', path: '/iframe.html?id=components-toast--error' },
+  { name: 'FilePreview-Text', path: '/iframe.html?id=components-filepreview--text-file' },
+  { name: 'FilePreview-Image', path: '/iframe.html?id=components-filepreview--image-file' },
+]
+
+for (const story of STORIES) {
+  test(`Visual: ${story.name}`, async ({ page }) => {
+    await page.goto(story.path)
+    await page.waitForLoadState('networkidle')
+    await expect(page).toHaveScreenshot(`${story.name}.png`)
+  })
+}