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/send_tab.cpp

@@ -821,7 +821,7 @@ void RenderSendConfirmPopup(App* app) {
         if (s_sending) {
             Type().text(TypeStyle::Body2, TR("sending"));
         } else {
-            if (TactileButton(TR("confirm_and_send"), ImVec2(S.button("tabs.send", "confirm-button").width, std::max(schema::UI().drawElement("tabs.send", "confirm-btn-min-height").size, schema::UI().drawElement("tabs.send", "confirm-btn-base-height").size * popVs)), S.resolveFont(S.button("tabs.send", "confirm-button").font))) {
+            if (TactileButton(TR("confirm_and_send"), ImVec2(S.button("tabs.send", "confirm-button").width * Layout::dpiScale(), std::max(schema::UI().drawElement("tabs.send", "confirm-btn-min-height").size, schema::UI().drawElement("tabs.send", "confirm-btn-base-height").size * popVs)), S.resolveFont(S.button("tabs.send", "confirm-button").font))) {
               // Re-validate against LIVE state — the confirm dialog persists across frames, so the
               // balance could have dropped or sync (re)started (or the fee bumped total over available)
               // since Review. Don't broadcast a now-invalid transaction.
@@ -874,7 +874,7 @@ void RenderSendConfirmPopup(App* app) {
               }
             }
             ImGui::SameLine();
-            if (TactileButton(TR("cancel"), ImVec2(S.button("tabs.send", "cancel-button").width, std::max(schema::UI().drawElement("tabs.send", "confirm-btn-min-height").size, schema::UI().drawElement("tabs.send", "confirm-btn-base-height").size * popVs)), S.resolveFont(S.button("tabs.send", "cancel-button").font))) {
+            if (TactileButton(TR("cancel"), ImVec2(S.button("tabs.send", "cancel-button").width * Layout::dpiScale(), std::max(schema::UI().drawElement("tabs.send", "confirm-btn-min-height").size, schema::UI().drawElement("tabs.send", "confirm-btn-base-height").size * popVs)), S.resolveFont(S.button("tabs.send", "cancel-button").font))) {
                 s_show_confirm = false;
             }
         }