fix(ui): consistent hashrate units, full-address tooltips, drop dead vars

- Balance card hashrate now uses the shared FormatHashrate() (TH/GH/MH/KH/H)
  instead of a bespoke two-tier KH/s formatter.
- Recent-tx rows show the full untruncated address on hover — two z-addresses can
  truncate to the same first/last window — and the truncate helpers guard maxLen<=3.
- Remove the unused viewTop/viewBot "viewport culling" locals in the tx list
  (pagination already bounds per-frame work).

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

src/ui/windows/transactions_tab.cpp

@@ -626,11 +626,7 @@ void RenderTransactionsTab(App* app)
                 scrollY    = ImGui::GetScrollY();
                 scrollMaxY = ImGui::GetScrollMaxY();
 
-                // Viewport culling bounds
-                float viewTop = scrollY;
-                float viewBot = scrollY + ImGui::GetWindowHeight();
-
-                // Render only the current page slice
+                // Render only the current page slice (pagination already bounds per-frame work)
                 for (int fi = pageStart; fi < pageEnd; fi++) {
                     size_t i = filtered_indices[fi];
                     const auto& tx = display_txns[i];