docs: mark repo deprecated; point at uPortal-start retirement PR (#320)

Problem: of the eleven widgets this repo ships, seven depend on
Google APIs that were sunset years ago (Google Loader 2015,
Maps v3.6 unsupported, Google Gadgets ~2016) and the remaining
widgets are JSP demos, trivial date/dictionary/embed shapes, or
already-in-uPortal-core (AppLauncherPortlet). The repo continues
to draw renovate-driven dependency-bump churn for code that
nobody can run usefully.

Goal: signal the deprecation clearly to anyone arriving at the
repo and to deployers still pinning a version, and point at the
uPortal-start PR that drops the overlay from the default
quickstart bundle.

Changes:
- README.md: insert a "DEPRECATED -- no longer maintained" block
  at the top with the rationale, the recommended deployer action
  (remove overlay, drop quickstart definitions binding to
  `/jasig-widget-portlets`), and a pointer at
  uPortal-Project/uPortal-start#696. Original README content is
  preserved below the divider for historical context.

Notes: the repo will remain on GitHub for historical reference
but receives no further releases. Subscribers who still depend
on the dictionary, calendar, or youtube widget shapes can have
them ported to small Lit web components on request -- the
shapes are trivial.

Author: bjagg

README.md

@@ -1,3 +1,15 @@
+## DEPRECATED -- no longer maintained
+
+This repository is deprecated and will not receive further updates. Of the eleven widgets it bundles, seven depend on Google APIs that were sunset years ago (Google Loader 2015, Maps v3.6, Google Gadgets ~2016); the remaining widgets are JSP demos, trivial date/dictionary/embed shapes, or have been absorbed into uPortal core (`AppLauncherPortlet`).
+
+uPortal-start no longer ships `JasigWidgetPortlets` in the default overlay set (see [uPortal-Project/uPortal-start#696](https://github.com/uPortal-Project/uPortal-start/pull/696)).
+
+**Recommended action for deployers:** remove this overlay from your deployment and drop any quickstart portlet definitions that bind to `/jasig-widget-portlets`. If you still actively use the dictionary, calendar, or youtube widget shapes, open an issue -- they can be ported to a small Lit web component on request.
+
+The repository will remain on GitHub for historical reference but receives no further releases.
+
+---
+
 # Jasig Widget Portlets
 
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/org.jasig.portlet/jasig-widget-portlets/badge.svg)](https://maven-badges.herokuapp.com/maven-central/org.jasig.portlet/jasig-widget-portlets)