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/network_tab.cpp

@@ -93,9 +93,12 @@ void RenderLiteNetworkTab(App* app)
         const bool connected = ws.connected;
         ImDrawList* sdl = ImGui::GetWindowDrawList();
         const float panelH = 56.0f * dp;
-        const float panelW = ImGui::GetContentRegionAvail().x;
+        const float availPanelW = ImGui::GetContentRegionAvail().x;
+        const float panelW = std::min(1000.0f * dp, availPanelW);
+        const float panelOffsetX = std::max(0.0f, (availPanelW - panelW) * 0.5f);
         const float pad2 = 12.0f * dp;
         ImVec2 pMin = ImGui::GetCursorScreenPos();
+        pMin.x += panelOffsetX;
         ImVec2 pMax(pMin.x + panelW, pMin.y + panelH);
         GlassPanelSpec sspec; sspec.rounding = 8.0f * dp;
         DrawGlassPanel(sdl, pMin, pMax, sspec);
@@ -150,7 +153,7 @@ void RenderLiteNetworkTab(App* app)
                                    Primary(), barH * 0.5f);
         }
 
-        ImGui::Dummy(ImVec2(panelW, panelH));  // reserve the panel (proper boundary growth)
+        ImGui::Dummy(ImVec2(availPanelW, panelH));  // reserve the full row (proper boundary growth)
         ImGui::Spacing();
     }
 
@@ -174,8 +177,8 @@ void RenderLiteNetworkTab(App* app)
     {
         const float availW = ImGui::GetContentRegionAvail().x;
         const float addBtnW = 80.0f * dp;
-        const float urlW = (availW - addBtnW - 16.0f * dp) * 0.6f;
-        const float lblW = (availW - addBtnW - 16.0f * dp) * 0.4f;
+        const float urlW = std::min(550.0f * dp, (availW - addBtnW - 16.0f * dp) * 0.6f);
+        const float lblW = std::min(300.0f * dp, (availW - addBtnW - 16.0f * dp) * 0.4f);
         ImGui::SetNextItemWidth(urlW);
         ImGui::InputTextWithHint("##LiteAddUrl", TR("lite_net_add_url_hint"), s_addUrl, sizeof(s_addUrl));
         ImGui::SameLine();
@@ -236,8 +239,11 @@ void RenderLiteNetworkTab(App* app)
         auto it = probe.find(sv.url);
         if (it != probe.end()) pr = it->second;
 
-        const float cardW = ImGui::GetContentRegionAvail().x;
+        const float availCardW = ImGui::GetContentRegionAvail().x;
+        const float cardW = std::min(1000.0f * dp, availCardW);
+        const float cardOffsetX = std::max(0.0f, (availCardW - cardW) * 0.5f);
         ImVec2 cardMin = ImGui::GetCursorScreenPos();
+        cardMin.x += cardOffsetX;
         ImVec2 cardMax(cardMin.x + cardW, cardMin.y + cardH);
         const float rnd = 8.0f * dp;
         const float cardBtnW = cardW - hideW;
@@ -326,8 +332,10 @@ void RenderLiteNetworkTab(App* app)
 
         // Advance to the next card via a real item (Dummy) below the card, so the scroll region's
         // content height actually grows — ImGui won't extend bounds from a bare SetCursorScreenPos.
-        ImGui::SetCursorScreenPos(ImVec2(cardMin.x, cardMax.y));
-        ImGui::Dummy(ImVec2(cardW, gap));
+        // Reset X to the (unshifted) region origin so next card's GetContentRegionAvail() isn't
+        // cumulatively narrowed by this card's centering offset.
+        ImGui::SetCursorScreenPos(ImVec2(cardMin.x - cardOffsetX, cardMax.y));
+        ImGui::Dummy(ImVec2(availCardW, gap));
     };
 
     // ── Visible servers ────────────────────────────────────────────────────────