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/status-bar/status-bar.ts

@@ -12,7 +12,7 @@ import { TransfersService } from '../transfers.service';
   imports: [NgIcon],
   template: `
     <div
-      class="flex h-6 items-center justify-between gap-4 border-t border-border px-3 text-[11px] text-muted-foreground select-none"
+      class="flex h-6 items-center justify-between gap-4 border-t border-border bg-chrome px-3 text-[11px] text-muted-foreground select-none"
     >
       <!-- transfers summary; click toggles the detailed list -->
       <button