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/transfer-bar/transfer-bar.html

@@ -1,5 +1,5 @@
 @if (transfers.expanded() && transfers.hasJobs()) {
-  <div class="flex items-center justify-between border-t border-border px-3 py-1 text-[11px] text-muted-foreground">
+  <div class="flex items-center justify-between border-t border-border bg-chrome px-3 py-1 text-[11px] text-muted-foreground">
     <span>
       {{ i18n.t('transfer.summary', { active: transfers.activeJobs().length, finished: transfers.finishedJobs().length }) }}
     </span>
@@ -11,7 +11,7 @@
       <ng-icon name="mynaTrash" size="0.75rem" /> {{ i18n.t('transfer.clearFinished') }}
     </button>
   </div>
-  <div class="max-h-40 overflow-y-auto border-t border-border">
+  <div class="max-h-40 overflow-y-auto border-t border-border bg-chrome">
     @for (job of transfers.jobs(); track job.id) {
       <div class="flex items-center gap-2 px-3 py-1.5 text-xs">
         <ng-icon [name]="stateIcon(job)" size="0.95rem" [class]="stateClass(job)" />