fix(lite): surface auto-open failures instead of a silent disconnected spinner

The startup auto-open of an existing lite wallet discarded openWallet()'s result,
so when initialize_existing failed (e.g. the lightwalletd server is unreachable)
the UI just showed a "disconnected" spinner with no reason — and DEBUG_LOGF is
compiled out of release builds, so there was no way to see why. Capture the
failure: store the reason, show it in the Network tab status line (in place of
"no wallet open"), and raise a notification. Cleared once a wallet opens.

This doesn't change open behaviour — it makes a stuck open diagnosable.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/windows/network_tab.cpp

@@ -122,10 +122,14 @@ void RenderLiteNetworkTab(App* app)
                      OnSurfaceMedium(), inUse.c_str());
 
         // Bottom row: sync detail + (while syncing) a thin progress bar.
-        char syncBuf[96];
-        if (!connected)
-            snprintf(syncBuf, sizeof(syncBuf), "%s: %s", TR("lite_net_sync_label"), TR("lite_net_no_wallet"));
-        else if (sync.syncing)
+        char syncBuf[160];
+        if (!connected) {
+            // If an auto-open actually failed, show why (e.g. server unreachable) instead of a
+            // bare "no wallet open" — otherwise the disconnected state is silent/confusing.
+            const std::string& openErr = app->liteOpenError();
+            snprintf(syncBuf, sizeof(syncBuf), "%s: %s", TR("lite_net_sync_label"),
+                     openErr.empty() ? TR("lite_net_no_wallet") : openErr.c_str());
+        } else if (sync.syncing)
             snprintf(syncBuf, sizeof(syncBuf), "%s: %.1f%%  ·  %d / %d", TR("lite_net_sync_label"),
                      sync.verification_progress * 100.0, sync.blocks, sync.headers);
         else