refactor: move the portal home into its own overzicht context (RD-03)

The dashboard page lived inside registratie, a context with no permitted
outbound edges. Two of its sections do cross-context navigation: action
links to herregistratie/intake/brief/concepts, and an admin links section
that imported ADMIN_LINKS directly from the app shell.

Move the page and these two navigation sections into a new overzicht
context. Declare overzicht: ['registratie'] as the one sanctioned edge, so
the four data sections that stay in registratie/ui/dashboard/ remain
reachable. The route stays at /dashboard: it is a user-visible URL and four
e2e specs assert it, so only the import path and class name change.

beheer-links.section.ts now injects HEADER_ADMIN_LINKS, the same token the
site header uses, instead of importing the app shell's nav config directly.

Used npm run gen:context and corrected its three known-wrong outputs: the
overzicht: [] edge, the scaffolded overzicht.page.ts (the real page is the
moved dashboard.page.ts), and the scaffolded path: 'overzicht' route.

Verified the boundary is enforced, not decorative: a temporary import of a
herregistratie file into overzicht.page.ts makes dep:check fail, as
expected, then reverted.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/ssp/tsconfig.json

@@ -6,6 +6,7 @@
   "compilerOptions": {
     "baseUrl": ".",
     "paths": {
+      "@overzicht/*": ["src/app/overzicht/*"],
       "@shared/*": ["../../libs/shared/src/*"],
       "@beheer/*": ["../../libs/beheer/src/*"],
       "@auth/*": ["src/app/auth/*"],