refactor(ui): extract shared ProgressBar / CopyableTextOverlay / DrawPill helpers

UI-standardization audit: three draw patterns were copy-pasted across tabs and
dialogs. Promote each to a material:: helper and adopt at every verbatim site.
Output is pixel-identical (same colors/geometry threaded through as params).

- material::DrawProgressBar / ProgressBar — replaces 3 byte-identical rounded
  fill bars in the daemon/xmrig/bootstrap download dialogs.
- material::CopyableTextOverlay — the click-to-copy affordance (hit button +
  hand cursor + tooltip + hover underline + clipboard) shared by the peers
  best-block hash and the 3 mining stats (difficulty/block/address). Returns
  "copied this frame" so callers keep their own toast (no ui-layer dependency).
- material::DrawPill / PillSize — rounded bg + optional border + inset text
  badge, shared by the explorer status pill, the market Z/T chip, and the
  network official/custom tag.

Divergent one-offs left in place (transactions status pills use schema rounding
around pre-positioned multi-line text; the mining filter-pill is a button bg).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/windows/bootstrap_download_dialog.h

@@ -162,18 +162,7 @@ private:
         ImGui::Spacing();
 
         // Progress bar
-        float barH = 8.0f * dp;
-        float barW = ImGui::GetContentRegionAvail().x;
-        ImVec2 barMin = ImGui::GetCursorScreenPos();
-        ImVec2 barMax(barMin.x + barW, barMin.y + barH);
-        ImDrawList* dl = ImGui::GetWindowDrawList();
-        dl->AddRectFilled(barMin, barMax, IM_COL32(255, 255, 255, 30), 4.0f * dp);
-        float fillW = barW * (prog.percent / 100.0f);
-        if (fillW > 0) {
-            dl->AddRectFilled(barMin, ImVec2(barMin.x + fillW, barMax.y),
-                              Primary(), 4.0f * dp);
-        }
-        ImGui::Dummy(ImVec2(0, barH));
+        material::ProgressBar(ImGui::GetContentRegionAvail().x, 8.0f * dp, prog.percent / 100.0f);
         ImGui::Spacing();
 
         // Percent + status text