refactor(SIGPG-7327): remove invariant dependency in favor of native …

[khamiltonuk]

fixes https://jira.tools.sap/browse/SIGPG-7327

What changed

• Replace all invariant() calls with native if/throw Error statements
• Removing the invariant and @types/invariant packages from dependencies.

How to test

• Open the app everything
• Pipeline should go green
  • npm run lint — passes with zero warnings
  • npm run test — all 204 Cypress component tests pass
  • npm run test:ssr — both SSR tests pass
  • Verify invariant is no longer in node_modules after a fresh npm ci should work

Notes

• invariant(condition, message) and if (!condition) throw new Error(message) have identical runtime behavior, so this is a pure dependency removal with no functional change.
• This removes two production dependencies (invariant, @types/invariant), reducing bundle size and the project's supply chain surface.