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/form/Settings.test.ts

@@ -53,6 +53,14 @@ describe('settings index (D-21)', () => {
     expect(link.text()).toBe('Search')
     expect(wrapper.find('[data-settings-group] h2').exists()).toBe(false)
   })
+
+  it('opens a controller-link entry on its controller route and keeps singleton links', async () => {
+    const link = { ...settingsFixture.list.data[0]!, code: 'locales', label: 'Locales', model: '', controller: 'acme.demo.locales' }
+    setSettings([...settingsFixture.list.data, link])
+    const { wrapper } = await mountApp('/settings', routes())
+    expect(wrapper.find('[data-settings="locales"]').attributes('href')).toMatch(/\/acme\/demo\/locales$/)
+    expect(wrapper.find('[data-settings="mail"]').attributes('href')).toBe('/settings/mail')
+  })
 })
 
 describe('settings form (D-21)', () => {