feat: add Case Studies page with 6 production case studies

- 6 detailed case studies: AI reconciliation, MT5 EA, Meta Ads AI,
  Web3 settlement, SaaS dashboard rebuild, VPS infra cost-cut
- Each with challenge/solution/results/stack/quote
- List view (click-to-expand detail) + metrics highlighted
- Route #/case-studies + nav link added
- Bump script cache-bust v5 → v6

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

src/nav.jsx

@@ -1,9 +1,9 @@
 // Top nav — minimal, sticky, blurred — mobile-responsive
 const NAV_LINKS = [
   { id: "services", label: "Services", url: "#/services" },
+  { id: "case-studies", label: "Case Studies", url: "#/case-studies" },
   { id: "pricing", label: "Pricing", url: "#/pricing" },
   { id: "blog", label: "Blog", url: "#/blog" },
-  { id: "timeline", label: "Timeline", url: "#/timeline" },
   { id: "contact", label: "Contact", url: "#/contact" },
 ]