feat(notes): surface GitHub auth-expired state on freshness badge

Show a cloud-lock badge with a re-sign-in tooltip when the freshness
check resolves to unauthorized, and toast on badge click so the user
gets explicit feedback instead of a silent retry-loop.

src/components/StackedNote.vue

@@ -228,6 +228,9 @@ const onBadgeClick = async () => {
   try {
     if (freshnessStatus.value !== "outdated") {
       await checkFreshness()
+      if (freshnessStatus.value === "unauthorized") {
+        errorMessage("🔐 GitHub auth expired — please sign in again")
+      }
       return
     }
 
@@ -241,6 +244,10 @@ const onBadgeClick = async () => {
     if (newRaw !== null) {
       rawContent.value = newRaw
       initialRawContent.value = newRaw
+      return
+    }
+    if (freshnessStatus.value === "unauthorized") {
+      errorMessage("🔐 GitHub auth expired — please sign in again")
     }
   } catch (error) {
     console.error("freshness badge click failed", error)