feat(frontend-plugin-api): add titleRouteRef to PageBlueprint

Add `titleRouteRef` to `PageLayoutProps` so the plugin header title
links back to the plugin root. `PageBlueprint` resolves it from
`plugin.routes.root` with fallback to `params.routeRef`.

- PageLayout swap resolves the title link via a conditional child
  component that calls `useRouteRef` only when a route ref exists
- Header actions get stable React keys via `cloneElement`

Signed-off-by: Johan Persson <johanopersson@gmail.com>

.changeset/hot-yaks-crash.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-app': patch
+---
+
+Updated the `PageLayout` swap to pass a clickable `titleLink` on the `PluginHeader`, resolved from the plugin's root route ref.

.changeset/lucky-things-write.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-plugin-api': patch
+---
+
+Added `titleLink` prop to `PageLayoutProps` so the plugin header title can link back to the plugin root.