Fix tvOS focus trap on empty Home after fresh install

Render a focusable empty state on tvOS Home when no sections have content,
with an "Open Sources" button that switches the sidebar selection. Without
a focusable view the tvOS focus engine had no target, leaving the sidebar
unreachable after the initial iCloud alert was dismissed.

Also wire the selectedSidebarItem onChange handler into the tvOS TabView,
which was missing and prevented programmatic sidebar selection.

Yattee/Localizable.xcstrings

@@ -3624,6 +3624,39 @@
         }
       }
     },
+    "home.tvos.empty.title" : {
+      "comment" : "tvOS Home empty-state title shown on fresh install",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Welcome to Yattee"
+          }
+        }
+      }
+    },
+    "home.tvos.empty.message" : {
+      "comment" : "tvOS Home empty-state message shown on fresh install",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Add a media source to start watching."
+          }
+        }
+      }
+    },
+    "home.tvos.empty.openSources" : {
+      "comment" : "tvOS Home empty-state button that opens the Sources screen",
+      "localizations" : {
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Open Sources"
+          }
+        }
+      }
+    },
     "home.history.clear" : {
       "comment" : "Clear history button",
       "localizations" : {