feat(history): show "Loading older history (N%)" during the initial bulk load

History streams in over many refresh cycles (the incremental shielded scan
walks every z-address), so the first batch appears long before the list is
complete — with no indication more is still coming. The existing loading banner
deliberately goes quiet once any rows are on screen.

Track whether the first full shielded scan has finished
(initial_history_scan_complete_) and, until it has, surface a progress percentage
(fraction of z-addresses scanned) in transactionRefreshProgressText() — which the
History tab already renders as its pulsing loading indicator. Goes quiet once the
first scan completes; routine per-block re-scans don't re-trigger it. Reset on a
full history invalidation (rescan / session reset) so it shows again on reload.

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

src/app.cpp

@@ -3704,6 +3704,20 @@ std::string App::transactionRefreshProgressText() const
         return buf;
     }
 
+    // Initial bulk history load: the incremental shielded scan streams older transactions in over
+    // many refresh cycles, so the first batch can appear long before the history is complete. Keep
+    // the user informed (with a %) even after rows are on screen, so they know it's still loading.
+    // Progress = fraction of z-addresses scanned at least once (monotonic). Goes quiet for good once
+    // the first full scan completes; routine per-block re-scans don't re-trigger it.
+    if (!initial_history_scan_complete_ && !state_.z_addresses.empty()) {
+        std::size_t total = state_.z_addresses.size();
+        std::size_t scanned = std::min(shielded_history_scan_heights_.size(), total);
+        int pct = total > 0 ? static_cast<int>((scanned * 100) / total) : 0;
+        if (pct > 99) pct = 99;  // 100% is the "complete" state, which suppresses the banner
+        snprintf(buf, sizeof(buf), TR("tx_loading_history_progress"), pct);
+        return buf;
+    }
+
     // Once history is on screen, stay quiet for routine background refreshes. The incremental
     // shielded-receive scan re-dirties transactions_dirty_ on EVERY new block (each block moves the
     // "scanned at tip" bar, invalidating prior per-address scans), so for a wallet with more