feat(ui): layout polish — fill dead space, pair/box/collapse, warning weight, dialog glass

Implements the layout-improvement suggestions from the layout audit (visual arrangement
only; no functionality added or removed):

- Send/Receive: the recent-activity list now grows to fill the space below the fixed
  compose/receive card (more history visible), with a centered empty-state when there is
  none — instead of leaving dead canvas.
- Shield/Merge: pair the Fee and UTXO-Limit fields on one row to tighten vertical rhythm.
- Market: extend + frame the portfolio group-list as one contained panel (with a bottom
  edge) and center its empty-state, closing the previously un-anchored gap.
- Overlay dialogs: raise the card glass fill/border alpha (35/50 -> 60/90 of 255) so the
  dialog card reads as a distinct surface over busy backdrops (global, all overlays).
- Wallets: size the list height to the actual wallet count instead of always reserving 7
  rows, removing the large gap before the scan/create prompts (still scrolls when many).
- Contacts: width-aware address truncation shows more of the address on wide rows.
- Transfer Funds: give the "sends the full balance" warning a warning icon + color so the
  stakes stand out from the neutral result-preview lines.
- First-run wizard: collapse a completed Step 1 (Appearance) to the compact pill like
  Step 2, so a finished step is no longer taller than the active one.
- Explorer: distribute the Chain card's two stats to match the density of the sibling
  metrics grid.
- Validate Address: a "Results will appear here" caption fills the pre-interaction blank.
- Change Passphrase: add the warning banner its sibling security dialogs have.
- Migration ShowSeed: box the 24-word mnemonic grid (a GlassSectionScope behind the
  existing RenderSeedWordGrid) so the critical secret reads as a distinct artifact —
  purely visual, no seed/logic/state change.

Verified at 1280 across full-node + Lite + Windows (ctest green) and an adversarial diff
review (clean). New i18n key backfilled into all 8 languages.

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

src/ui/windows/explorer_tab.cpp

@@ -620,7 +620,16 @@ static void renderChainStats(App* app, float availWidth) {
             ImVec2(cardMin.x + pad, cardMin.y + pad * 0.5f), Primary(), TR("explorer_chain_stats"));
         drawStatusPill(cardMin, cardW);
 
-        float labelY = cardMin.y + pad * 0.5f + headerH + Layout::spacingLg();
+        // Distribute the two stat blocks (Height, Best Block) evenly through the
+        // content region so the card matches the density of the sibling 2x2 metric
+        // grid instead of pinning Height to the top and Best Block to the bottom
+        // edge with a large empty gap between them.
+        float contentTop = cardMin.y + pad * 0.5f + headerH;
+        float contentBottom = cardMax.y - pad;
+        float blockGap = std::max(Layout::spacingMd(),
+            (contentBottom - contentTop - heroLineH - hashLineH) / 3.0f);
+
+        float labelY = contentTop + blockGap;
         dl->AddText(capFont, capFont->LegacySize,
             ImVec2(cardMin.x + pad, labelY), OnSurfaceMedium(), TR("explorer_block_height"));
 
@@ -640,7 +649,7 @@ static void renderChainStats(App* app, float availWidth) {
                 ImVec2(cardMin.x + pad + barW * progress, barY + barH), WithAlpha(Warning(), 180), barH * 0.5f);
         }
 
-        float hashLabelY = cardMax.y - pad - hashLineH;
+        float hashLabelY = labelY + heroLineH + blockGap;
         dl->AddText(capFont, capFont->LegacySize,
             ImVec2(cardMin.x + pad, hashLabelY), OnSurfaceMedium(), TR("peers_best_block"));