feat(gci): add Gesamt-Compliance-Index scoring engine and dashboard

Implements the 4-level GCI scoring model (Module -> Risk-Weighted -> Regulation Area -> Final GCI)
with DSGVO, NIS2, ISO 27001, and EU AI Act integration.

Backend:
- 9 Go files: engine, models, weights, validity, NIS2 roles/scoring, ISO mapping/gap-analysis, mock data
- GCI handlers with 13 API endpoints under /sdk/v1/gci/
- Routes registered in main.go

Frontend:
- TypeScript types, API client, Next.js API proxy
- Dashboard page with 6 tabs (Overview, Breakdown, NIS2, ISO 27001, Matrix, Audit Trail)
- Sidebar navigation entry

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

admin-compliance/components/sdk/Sidebar/SDKSidebar.tsx

@@ -561,6 +561,20 @@ export function SDKSidebar({ collapsed = false, onCollapsedChange }: SDKSidebarP
             isActive={pathname === '/sdk/reporting'}
             collapsed={collapsed}
           />
+          <AdditionalModuleItem
+            href="/sdk/gci"
+            icon={
+              <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2}
+                  d="M11 3.055A9.001 9.001 0 1020.945 13H11V3.055z" />
+                <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2}
+                  d="M20.488 9H15V3.512A9.025 9.025 0 0120.488 9z" />
+              </svg>
+            }
+            label="GCI Score"
+            isActive={pathname === '/sdk/gci'}
+            collapsed={collapsed}
+          />
           <AdditionalModuleItem
             href="/sdk/industry-templates"
             icon={