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/chat_tab.cpp

@@ -12,6 +12,7 @@
 #include "../../util/i18n.h"
 #include "../material/colors.h"
 #include "../material/type.h"
+#include "../layout.h"   // Layout::dpiScale()
 #include "imgui.h"
 
 #include <algorithm>
@@ -134,8 +135,11 @@ void RenderChatTab(App* app)
 
     const ImVec2 avail = ImGui::GetContentRegionAvail();
     const float listW = std::clamp(avail.x * 0.32f, 220.0f, 360.0f);
-    const float pad = 10.0f;
-    const float rowH = 52.0f;
+    // Row geometry is logical px — scale by dpiScale() so rows/padding grow with the (DPI-scaled)
+    // fonts. Left raw, at higher DPI the row was too short for the enlarged text and the preview's
+    // right margin (rowW - pad) shrank to ~zero, clipping the last glyph mid-word.
+    const float pad = 10.0f * Layout::dpiScale();
+    const float rowH = 52.0f * Layout::dpiScale();
 
     ImFont* nameFont = material::Type().body2();
     ImFont* metaFont = material::Type().caption();