fix(ui): DPI-scale hand-drawn overlays + freeze sweep demo state

Hand-drawn absolute geometry (dl->AddText offsets, SetNextWindowSize,
explicit ImVec2 button widths, SameLine strides) is immune to the app's
DPI machinery (font-atlas rebuild + ScaleAllSizes), so several overlays
rendered native-size (tiny) on HiDPI / Windows 150% displays. Multiply the
raw logical-px geometry by Layout::dpiScale():

- seed_display: content-aware, DPI-scaled seed-grid column stride (a raw
  130px stride let words collide with the next column's index at 150%)
- lock screen: card/logo/input/unlock-button + all vertical offsets
- migrate-to-seed + seed-backup dialogs: button widths
- send-confirm: confirm/cancel button widths
- about dialog: value-column x, edition inset, link/close button widths
- chat conversation list: row height + padding (fixes the preview clip)

Also freeze demo state during the full UI sweep: guard App::update() on
capture_mode_ so a running daemon's refresh can't clobber the injected
demo state (it blanked Send/Receive/History with a CDB error mid-sweep).

Verified on Windows 4K@150% and locally at font_scale=1.5 (same
dpiScale()==1.5 code path). Adds a DPI-scaling convention note to CLAUDE.md.

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

src/ui/windows/seed_display.h

@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "imgui.h"
+#include "../layout.h"   // Layout::dpiScale()
 
 namespace dragonx {
 namespace ui {
@@ -31,14 +32,26 @@ inline std::vector<std::string> SplitSeedWords(const std::string& phrase)
 }
 
 // Render the words as a numbered 4-column grid (matches the lite welcome wizard layout).
+// The column stride is sized to the widest "NN. word" cell and scaled by dpiScale(): a raw px
+// stride collided with the next column's index once the font grew at higher DPI / font scale
+// (e.g. at 150% "13. elevator" ran straight into "14."). Sizing to content keeps a gap at any
+// scale and for any word length.
 inline void RenderSeedWordGrid(const std::vector<std::string>& words, float colSpacingPx = 130.0f)
 {
+    const float dp = Layout::dpiScale();
+    float colStride = colSpacingPx * dp;
+    for (size_t i = 0; i < words.size(); ++i) {
+        char cell[96];
+        std::snprintf(cell, sizeof(cell), "%2zu. %s", i + 1, words[i].c_str());
+        const float need = ImGui::CalcTextSize(cell).x + 20.0f * dp;  // cell width + inter-column gap
+        if (need > colStride) colStride = need;
+    }
     for (size_t i = 0; i < words.size(); ++i) {
         char cell[96];
         std::snprintf(cell, sizeof(cell), "%2zu. %s", i + 1, words[i].c_str());
         ImGui::TextUnformatted(cell);
         if ((i % 4) != 3 && i + 1 < words.size())
-            ImGui::SameLine(((i % 4) + 1) * colSpacingPx);
+            ImGui::SameLine(((i % 4) + 1) * colStride);
     }
 }