feat(admin): open controller-link settings entries from the settings index

A settings entry with a controller opens that controller's route from
its card (settingsPath); singleton cards still open /settings/<code>.
On a linked controller with no navigation entry of its own the rail
marks Settings current, the breadcrumbs read Settings > entry label
(plus the record title on record and create routes) and the page title
uses the entry label. The settings docs describe the admin behaviour;
the embedded admin shell is rebuilt.

admin/tests/shell/PluginRail.test.ts

@@ -59,6 +59,20 @@ describe('plugin rail', () => {
     expect(link.attributes('aria-current')).toBe('page')
   })
 
+  it('marks Ustawienia current on a settings-linked controller without a navigation entry', async () => {
+    const locales = { ...settingsFixture.list.data[0]!, code: 'locales', label: 'Locales', model: '', controller: 'acme.lang.locales' }
+    const widgets = { ...locales, code: 'widgets', label: 'Widgets', controller: 'acme.demo.widgets' }
+    setSettings([...settingsFixture.list.data, locales, widgets])
+    const { wrapper } = await mountRail('/acme/lang/locales')
+    expect(wrapper.find('[data-rail-settings]').attributes('aria-current')).toBe('page')
+    expect(wrapper.findAll('[data-rail-item][aria-current="page"]')).toHaveLength(0)
+
+    // A linked controller that also has a navigation entry keeps its plugin.
+    const nav = await mountRail('/acme/demo/widgets')
+    expect(nav.wrapper.find('[data-rail-settings]').attributes('aria-current')).toBeUndefined()
+    expect(nav.wrapper.find('[data-rail-item="demo"]').attributes('aria-current')).toBe('page')
+  })
+
   it('offers menu semantics and the expand button after a manual collapse', async () => {
     const { wrapper } = await mountRail('/acme/demo/widgets')
     expect(wrapper.find('[data-sidebar-expand]').exists()).toBe(false)