fix(onboarding): seed screen's lock stays steady through silent retries

The catch block dropped `loading` before branching, so every failed poll
unmounted the lock icon and status text for the 4s retry gap — the screen
flashed in and out on a live install test (zaza-optiplex, 2026-08-09).
`loading` now stays true across isServerStartingError retries; only success
or a genuine failure dismisses the waiting state.

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

neode-ui/src/views/OnboardingSeedGenerate.vue

@@ -259,9 +259,11 @@ async function generateSeed() {
     loading.value = false
     waitingForServer.value = false
   } catch (err) {
-    loading.value = false
     if (isServerStartingError(err)) {
-      // Backend not ready yet — keep waiting, retry silently.
+      // Backend not ready yet — keep waiting, retry silently. `loading` stays
+      // true through the whole retry loop: dropping it here unmounts the lock
+      // icon and status text for the 4s between attempts, which reads as the
+      // screen flashing in and out (reported on a live install test).
       if (!waitingForServer.value) {
         waitingForServer.value = true
         startElapsedTimer()
@@ -270,6 +272,7 @@ async function generateSeed() {
     } else {
       // Genuine failure — stop the silent loop and surface it with a manual retry.
       stopTimers()
+      loading.value = false
       waitingForServer.value = false
       errorMessage.value = err instanceof Error ? err.message : 'Failed to generate seed'
     }