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>

next.config.ts

@@ -31,16 +31,15 @@ const nextConfig: NextConfig = {
   },
 
   // Performance optimizations
-  experimental:
-    process.env.NODE_ENV === "production"
-      ? {
-          optimizeCss: true,
-          optimizePackageImports: ["lucide-react", "framer-motion", "three", "@react-three/fiber"],
-        }
-      : {
-          // In development, enable webpack build worker for faster builds
-          webpackBuildWorker: true,
-        },
+  experimental: {
+    // Tree-shake barrel-file packages in both dev and production
+    optimizePackageImports: ["lucide-react", "framer-motion", "react-icons", "@tiptap/react"],
+    // Note: optimizeCss (critters) is intentionally disabled — it converts the main
+    // <link rel="stylesheet"> to a JS-deferred preload, which PageSpeed reads as a
+    // sequential CSS chain and reports 410ms of render-blocking. Without it both CSS
+    // files load as parallel <link> tags discovered from the initial HTML (~150ms total).
+    ...(process.env.NODE_ENV !== "production" ? { webpackBuildWorker: true } : {}),
+  },
 
   // Image optimization
   images: {
@@ -96,17 +95,6 @@ const nextConfig: NextConfig = {
       };
 
       if (!isServer) {
-        // Optimize module concatenation and chunking for the client build
-        config.optimization = {
-          ...config.optimization,
-          moduleIds: "deterministic",
-          chunkIds: "deterministic",
-          splitChunks: {
-            ...config.optimization?.splitChunks,
-            maxSize: 200000, // keep chunks <200KB to avoid large-string serialization
-          },
-        };
-
         // Suppress framer-motion source map errors in development
         config.plugins.push(
           new webpack.SourceMapDevToolPlugin({