docs(reference-app): restructure the README around seeing it work

Leads with the visual walkthrough and a one-command quick start, adds a navigation table mapping each feature to its controller/service and the test that proves it, and moves the conceptual OAuth/OIDC background and the test-rig details down. Refreshes the stale (2022) OIDC example id_token and JWKS from a current run, normalized to the bootTestRun view (issuer localhost:4444, audience demo-client). Removes the task list and folds prerequisites into the quick start.

Author: ardetrick