Retone dark theme to warm gray #1a1a19 with layered surfaces

The dark palette was shadcn's cool zinc (#202023, hue ~286). Anchor it on
#1a1a19 instead — cds gray-830, a warm near-neutral (hue 107) — and retone
the whole dark neutral family to match, since a warm background under cool
panels clashes. Lightness ramp is preserved; chromatic tokens (destructive,
success, icon hues, accent formulas) and the light palette are untouched.

Also introduce --chrome so the app isn't one flat tone: frame strips (tab
bar, status bar, transfer bar, editor/manager header+footer, connection
sidebar) now sit one step below the content panes, with popovers and hover
above them — the standard dark-UI elevation order.

Dark ramp: #151514 chrome, #1a1a19 content, #20201f card, #2e2e2d hover;
the "darker" tone drops chrome to true black. Light gains only a zinc-50
chrome step.

Co-Authored-By: Claude <noreply@anthropic.com>

ui/src/app/editor-window/editor-window.html

@@ -13,7 +13,7 @@
     <!-- header: on macOS this row IS the titlebar (hiddenInset + drag region),
          elsewhere the native titlebar sits above and this is a compact strip -->
     <header
-      class="flex shrink-0 items-center gap-2 border-b border-border pr-2"
+      class="flex shrink-0 items-center gap-2 border-b border-border bg-chrome pr-2"
       [class.h-10]="isMacChrome"
       [class.pl-24]="isMacChrome"
       [class.electrobun-webkit-app-region-drag]="isMacChrome"
@@ -46,7 +46,7 @@
     </header>
 
     @if (findOpen()) {
-      <div class="flex shrink-0 items-center gap-2 border-b border-border px-3 py-1.5">
+      <div class="flex shrink-0 items-center gap-2 border-b border-border bg-chrome px-3 py-1.5">
         <ng-icon name="mynaSearch" size="0.85rem" class="shrink-0 text-muted-foreground" />
         <input
           #findBox
@@ -140,7 +140,7 @@
         ></textarea>
       </div>
 
-      <footer class="flex shrink-0 items-center gap-2 border-t border-border px-4 py-2">
+      <footer class="flex shrink-0 items-center gap-2 border-t border-border bg-chrome px-4 py-2">
         <span class="text-[11px] text-muted-foreground">{{ i18n.t('editor.shortcuts', { mod: modLabel }) }}</span>
         <span class="text-[11px] text-muted-foreground">·</span>
         <span class="text-[11px] tabular-nums text-muted-foreground">