perf: eliminate Three.js/WebGL, fix render-blocking CSS, add dev team agents

- Replace ShaderGradientBackground WebGL shader (3 static spheres) with pure
  CSS radial-gradient divs — moves from ClientProviders (deferred JS) to
  app/layout.tsx as a server component rendered in initial HTML. Eliminates
  @shadergradient/react, three, @react-three/fiber from the JS bundle.
  Removes chunks/7001 (~20s CPU eval) and the 39s main thread block.

- Remove optimizeCss/critters: it was converting <link rel="stylesheet"> to a
  JS-deferred preload, which PageSpeed read as a 410ms sequential CSS chain.
  Both CSS files now load as parallel <link> tags from initial HTML (~150ms).

- Update browserslist safari >= 15 → 15.4 (Array.prototype.at, Object.hasOwn
  are native in 15.4+; eliminates unnecessary SWC compatibility transforms).

- Delete orphaned app/styles/ghostContent.css (never imported anywhere, 3.7KB).

- Add .claude/ dev team setup: 5 subagents (frontend-dev, backend-dev, tester,
  code-reviewer, debugger), 3 skills (/add-section, /review-changes,
  /check-quality), 3 path-scoped rules, settings.json with auto-lint hook.

- Update CLAUDE.md with server/client orchestrator pattern, SSR animation
  safety rules, API route conventions, and improved command reference.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/rules/testing.md

@@ -0,0 +1,38 @@
+---
+paths:
+  - "**/__tests__/**/*.ts"
+  - "**/__tests__/**/*.tsx"
+  - "**/*.test.ts"
+  - "**/*.test.tsx"
+  - "e2e/**/*.spec.ts"
+---
+
+# Testing Rules
+
+## Jest environment
+- Global mocks are set up in `jest.setup.ts` — do NOT re-mock `matchMedia`, `IntersectionObserver`, or `NextResponse` in individual tests
+- Test env vars are pre-set: `DIRECTUS_URL`, `NEXT_PUBLIC_SITE_URL`
+- Always mock external API calls (Directus, n8n, PostgreSQL) — tests must work without running services
+
+## ESM modules
+If a new import causes "Must use import to load ES Module" errors, add the package to `transformIgnorePatterns` in `jest.config.ts`.
+
+## Server component tests
+```typescript
+// Server components return JSX, not a promise in React 19, but async ones need await
+const resolved = await MyServerComponent({ locale: 'en', ...props })
+render(resolved)
+```
+
+## next/image in tests
+Replace `next/image` with a plain `<img>` in test renders:
+```tsx
+// eslint-disable-next-line @next/next/no-img-element
+<img src={src} alt={alt} />
+```
+
+## Run commands
+- Single file: `npx jest path/to/test.tsx`
+- All unit tests: `npm run test`
+- Watch mode: `npm run test:watch`
+- Specific E2E: `npm run test:critical`, `npm run test:hydration`, `npm run test:accessibility`