feat(web): Classic UI link in Settings → System (#147)

Add a discoverable "Open Classic UI" link in the SPA's Settings → System
About card, pointing at /system/health (a real full-page navigation, not
the SPA's pushState router), so un-migrated Blazor-only admin screens
stay reachable now that root / redirects to the SPA.

Also add a lightweight "Opens in ChicoryTV" tooltip cue (small icon) on
the Blazor sidebar's redirecting MudNavLink entries (per
LegacyUiRedirects.Map), so it's clear before clicking which sidebar
entries leave the Blazor UI vs. stay in it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ErsatzTV/Locals/Shared/MainLayout.resx

@@ -141,6 +141,9 @@
     <data name="ButtonSettingsXmltv" xml:space="preserve">
         <value>XMLTV</value>
     </data>
+    <data name="ButtonOpensInChicoryTv" xml:space="preserve">
+        <value>Opens in ChicoryTV</value>
+    </data>
     <data name="ButtonSupport" xml:space="preserve">
         <value>Support</value>
     </data>