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>

app/components/ClientProviders.tsx

@@ -8,13 +8,8 @@ import ErrorBoundary from "@/components/ErrorBoundary";
 import { ConsentProvider } from "./ConsentProvider";
 import { ThemeProvider } from "./ThemeProvider";
 
-const BackgroundBlobs = dynamic(() => import("@/components/BackgroundBlobs").catch(() => ({ default: () => null })), {
-  ssr: false,
-  loading: () => null,
-});
-
-const ShaderGradientBackground = dynamic(
-  () => import("./ShaderGradientBackground").catch(() => ({ default: () => null })),
+const BackgroundBlobs = dynamic(
+  () => import("@/components/BackgroundBlobs").catch(() => ({ default: () => null })),
   { ssr: false, loading: () => null }
 );
 
@@ -52,17 +47,16 @@ function GatedProviders({
   children: React.ReactNode;
   mounted: boolean;
 }) {
-  // Defer heavy Three.js/WebGL background until after LCP
+  // Defer animated background blobs until after LCP
   const [deferredReady, setDeferredReady] = useState(false);
   useEffect(() => {
     if (!mounted) return;
-    // Safari < 16.4 lacks requestIdleCallback — fall back to setTimeout
     let id: ReturnType<typeof setTimeout> | number;
     if (typeof requestIdleCallback !== "undefined") {
       id = requestIdleCallback(() => setDeferredReady(true), { timeout: 5000 });
       return () => cancelIdleCallback(id as number);
     } else {
-      id = setTimeout(() => setDeferredReady(true), 1);
+      id = setTimeout(() => setDeferredReady(true), 200);
       return () => clearTimeout(id);
     }
   }, [mounted]);
@@ -71,7 +65,6 @@ function GatedProviders({
     <ErrorBoundary>
       <ToastProvider>
         {deferredReady && <BackgroundBlobs />}
-        {deferredReady && <ShaderGradientBackground />}
         <div className="relative z-10">{children}</div>
       </ToastProvider>
     </ErrorBoundary>