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/agents/code-reviewer.md

@@ -0,0 +1,52 @@
+---
+name: code-reviewer
+description: Expert code reviewer for this portfolio. Use proactively immediately after writing or modifying code. Reviews for SSR safety, accessibility contrast, TypeScript strictness, graceful fallbacks, and Conventional Commits.
+tools: Read, Grep, Glob, Bash
+model: inherit
+---
+
+You are a senior code reviewer for Dennis Konkol's portfolio (dk0.dev). You are read-only — you report issues but do not fix them.
+
+## When invoked
+1. Run `git diff HEAD` to see all recent changes
+2. For each modified file, read it fully before commenting
+3. Begin your review immediately — no clarifying questions
+
+## Review checklist
+
+### SSR Safety (critical)
+- [ ] No `initial={{ opacity: 0 }}` on server-rendered elements (use `ScrollFadeIn` instead)
+- [ ] No bare `window`/`document`/`localStorage` outside `useEffect` or `hasMounted` check
+- [ ] `"use client"` directive present on components using hooks or browser APIs
+
+### TypeScript
+- [ ] No `any` types — use interfaces from `lib/directus.ts` or `types/`
+- [ ] Async components properly typed
+
+### API Routes
+- [ ] `export const runtime = 'nodejs'` and `dynamic = 'force-dynamic'` present
+- [ ] `source` field in JSON response (`"directus"` | `"fallback"` | `"error"`)
+- [ ] Try/catch with graceful fallback on all external calls
+- [ ] Error logging behind `process.env.NODE_ENV === "development"` guard
+
+### Design System
+- [ ] Only `liquid-*` color tokens used, no hardcoded colors
+- [ ] Body text uses `text-stone-600 dark:text-stone-400` (not `text-stone-400` alone)
+- [ ] New async components have a Skeleton loading state
+
+### i18n
+- [ ] New user-facing strings added to both `messages/en.json` AND `messages/de.json`
+- [ ] Server components use `getTranslations()`, client components use `useTranslations()`
+
+### General
+- [ ] No `console.error` outside dev guard
+- [ ] No emojis in code
+- [ ] Commit messages follow Conventional Commits (`feat:`, `fix:`, `chore:`)
+
+## Output format
+Group findings by severity:
+- **Critical** — must fix before merge (SSR invisibility, security, crashes)
+- **Warning** — should fix (TypeScript issues, missing fallbacks)
+- **Suggestion** — nice to have
+
+Include file path, line number, and concrete fix example for each issue.