feat(ui): width-responsiveness — content max-width cap + per-surface form/input clamps

Wide/ultrawide (1440-3440px) responsiveness was unhealthy: no page/content-level
max-width cap existed, and every card/form/table derived width from raw
GetContentRegionAvail().x with floor-only clamps, so surfaces stretched edge-to-edge
(2000-3000px inputs, ballooning cards, giant grid cells, 2000px+ dead row-voids).

Root cause: adopt the (previously dead-code) clamp helpers.
- New Layout::kContentMaxWidth() (~1600dp, tunable via ui.toml [layout]
  content-max-width; <=0 disables). Cap ##ContentArea to it and center the column in
  wider windows — every tab derives from this child, so one change tames the app at
  wide widths. No-op below the cap (fills as before), so 1080p/1440p are unaffected.

Per-surface upper-clamps (std::min(cap*dp, expr), floors preserved) where a single
element is still too wide even within the capped column:
- Settings: Theme/Layout/Language combos, the font-scale slider (~3000px -> 360dp),
  the effect sliders, Explorer URL and RPC credential fields.
- Send / Receive: cap the compose / receive cards to a readable form width and center
  them (Indent(pad+offset) so the auto-layout fields align with the hand-drawn card);
  the recent-tx lists below keep the full column width.
- Chat message bubbles + composer, mining pool URL/payout inputs + stats left/right
  split, contacts search, and the lite-network add-server row / server cards / status
  panel (capped + centered).
- Wizard: vertically center the cards when they fit (was top-anchored, leaving a void
  on tall monitors), compensating the content-height measurement so it can't oscillate.

The 1600 cap also subsumes the fixed-4-column balance grids (~400px cards) and the
right-anchored row dead-gaps (voids shrink from ~2700px to ~800px), so those are left
to the cap rather than blind column/row redesigns.

Verified at 1024/1280 (and via a temporary 900dp cap to exercise the cap+center path,
since the test display clamps to 1280) across full-node + Lite + Windows (ctest green)
and an adversarial diff review (clean). The true wide/ultrawide look and the 1600dp cap
value still want eyes on a real wide monitor.

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

src/ui/windows/receive_tab.cpp

@@ -581,21 +581,34 @@ void RenderReceiveTab(App* app)
     // MAIN CARD — single glass panel (channel split like Send tab)
     // ================================================================
     {
+        // Cap + center the card so the address/amount column stops stretching while the
+        // QR plateaus. cardW never exceeds formW (only shrinks); leftover becomes margin.
+        // The RECENT RECEIVED list below stays on the uncapped formW (handled separately).
+        float cardDp = Layout::dpiScale();
+        float cardW = std::min(formW, 860.0f * cardDp);
+        float cardLeftX = ImGui::GetCursorScreenPos().x;
+        float cardOffsetX = std::max(0.0f, (formW - cardW) * 0.5f);
+        if (cardOffsetX > 0.0f)
+            ImGui::SetCursorPosX(ImGui::GetCursorPosX() + cardOffsetX);
+
         ImVec2 containerMin = ImGui::GetCursorScreenPos();
         float pad = Layout::spacingLg();
-        float innerW = formW - pad * 2;
+        float innerW = cardW - pad * 2;
         float innerGap = Layout::spacingLg();
 
         // Channel split: content on ch1, glass background on ch0
         dl->ChannelsSplit(2);
         dl->ChannelsSetCurrent(1);
 
-        ImGui::Indent(pad);
+        // Indent carries the centering offset too, so ImGui auto-layout content (the address
+        // dropdown/inputs/chips) lands at containerMin.x + pad — matching the hand-drawn geometry
+        // (glass panel / QR column) that keys off the offset containerMin.x.
+        ImGui::Indent(pad + cardOffsetX);
         ImGui::Dummy(ImVec2(0, pad)); // top padding
 
         // ---- ADDRESS DROPDOWN + QR CODE — side by side ----
         {
-            float qrColW = innerW * schema::UI().drawElement("tabs.receive", "qr-col-width-ratio").size;
+            float qrColW = std::min(innerW * schema::UI().drawElement("tabs.receive", "qr-col-width-ratio").size, 340.0f * cardDp);
             float colGap = Layout::spacingLg();
             float addrColW = innerW - qrColW - colGap;
             float qrColX = containerMin.x + pad + addrColW + colGap;
@@ -876,7 +889,7 @@ void RenderReceiveTab(App* app)
                                         S.drawElement("tabs.receive", "action-btn-height").size * vScale);
             float footerH = innerGap + actionBtnH + pad;
             float currentCardH = ImGui::GetCursorScreenPos().y - containerMin.y;
-            float targetCardH = std::min(Layout::mainCardTargetH(formW, vScale), recvCardCapH);
+            float targetCardH = std::min(Layout::mainCardTargetH(cardW, vScale), recvCardCapH);
             float footerTopH = targetCardH - footerH;
             if (currentCardH < footerTopH) {
                 ImGui::Dummy(ImVec2(0, footerTopH - currentCardH));
@@ -887,7 +900,7 @@ void RenderReceiveTab(App* app)
         {
             ImVec2 divPos = ImGui::GetCursorScreenPos();
             dl->AddLine(ImVec2(containerMin.x + pad, divPos.y),
-                        ImVec2(containerMin.x + formW - pad, divPos.y),
+                        ImVec2(containerMin.x + cardW - pad, divPos.y),
                         ImGui::GetColorU32(Divider()), S.drawElement("tabs.receive", "divider-thickness").size);
         }
         ImGui::Dummy(ImVec2(0, innerGap * 0.5f));
@@ -967,24 +980,26 @@ void RenderReceiveTab(App* app)
 
         // Bottom padding
         ImGui::Dummy(ImVec2(0, pad));
-        ImGui::Unindent(pad);
+        ImGui::Unindent(pad + cardOffsetX);
 
         // Enforce shared card height (matches QR-driven target), capped so the reserved
         // RECENT RECEIVED slice below stays on-screen at HiDPI.
         {
             float currentCardH = ImGui::GetCursorScreenPos().y - containerMin.y;
-            float targetCardH  = std::min(Layout::mainCardTargetH(formW, vScale), recvCardCapH);
+            float targetCardH  = std::min(Layout::mainCardTargetH(cardW, vScale), recvCardCapH);
             if (currentCardH < targetCardH)
                 ImGui::Dummy(ImVec2(0, targetCardH - currentCardH));
         }
 
         // Draw glass panel background on channel 0
-        ImVec2 containerMax(containerMin.x + formW, ImGui::GetCursorScreenPos().y);
+        ImVec2 containerMax(containerMin.x + cardW, ImGui::GetCursorScreenPos().y);
         dl->ChannelsSetCurrent(0);
         DrawGlassPanel(dl, containerMin, containerMax, glassSpec);
         dl->ChannelsMerge();
 
-        ImGui::SetCursorScreenPos(ImVec2(containerMin.x, containerMax.y));
+        // Restore the original (uncapped) left edge so RECENT RECEIVED below renders
+        // full-width as-is, unaffected by the card's centering offset.
+        ImGui::SetCursorScreenPos(ImVec2(cardLeftX, containerMax.y));
         ImGui::Dummy(ImVec2(formW, 0));
         ImGui::Dummy(ImVec2(0, Layout::spacingSm()));
     }