feat(marketing): /staerken page with 7 USPs from IACE strategy — Task #19

Long-form differentiator page covering the seven sales arguments from
project_marketing_website_3014_themes.md, all anchor-linkable for
sales decks:

  #1 engine          — Pattern-engine vs Excel-checklist
  #2 multi-markt     — One risk assessment, all markets (CE+US+CN+JP)
  #3 folgegefahren   — Operator-to-end-customer harm chain
  #4 public-domain   — OSHA/NIST/EUR-Lex/BAuA as legal anchor
  #5 audit-suite     — Engine self-introspection (cmd/iace-audit A-E)
  #6 made-in-germany — German export meets US Federal PD
  #7 tooling         — LLM gap-review as co-pilot, not robo-lawyer

Each section carries a "Belegt durch:" line pointing at the actual
codebase artifact behind the claim, so the page reads as audit-friendly
proof, not marketing fluff.

Below the 7 differentiators a competitor comparison table (BreakPilot
vs DesignSafe vs Pilz PASS vs Sick SD vs Sphera) and a closing block
explaining the R1/R2/R3 license architecture with a pointer to
/sdk/licenses.

Navbar updated to surface the page between Plattform and CE-Prozess.

This closes Task #19. With Task #29 + #7/#8 already in, the roadmap
post-licence-classification work is fully landed.

marketing-website/lib/sections.ts

@@ -1,6 +1,7 @@
 // Navbar links — route-based navigation
 export const navLinks = [
   { href: '/plattform', labelDe: 'Plattform', labelEn: 'Platform' },
+  { href: '/staerken', labelDe: 'Stärken', labelEn: 'Differentiators' },
   { href: '/ce-prozess', labelDe: 'CE-Prozess', labelEn: 'CE Process' },
   { href: '/product-compliance', labelDe: 'Product Compliance', labelEn: 'Product Compliance' },
   { href: '/architektur', labelDe: 'Architektur', labelEn: 'Architecture' },