Dark tone setting: grey Dark (default) vs near-black Darker

Tone row appears under Theme when the effective theme is dark.
Grey palette uses macOS-like #26262a background.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/app/tab-bar/tab-bar.ts

@@ -7,6 +7,7 @@ import { RpcService } from '../rpc.service';
 import { SettingsService } from '../settings.service';
 
 const THEMES = ['system', 'light', 'dark'] as const;
+const DARK_TONES = ['dark', 'darker'] as const;
 // Swatch colors are fixed mid-tones so every dot reads on both light and dark
 // cards (the live --primary values would vanish against one of them).
 const ACCENTS: readonly { value: AccentTone; swatch: string; label: string }[] = [
@@ -133,6 +134,25 @@ const CONCURRENCY_CHOICES = [2, 3, 4, 6, 8] as const;
             </div>
           </div>
 
+          @if (settings.effectiveDark()) {
+            <div class="mt-2.5 flex items-center justify-between gap-2">
+              <span class="text-xs text-muted-foreground">Tone</span>
+              <div class="flex rounded-md border border-border p-0.5">
+                @for (tone of darkTones; track tone) {
+                  <button
+                    (click)="settings.setDarkTone(tone)"
+                    class="rounded px-2 py-0.5 text-[11px] capitalize"
+                    [class.bg-accent]="settings.darkTone() === tone"
+                    [class.text-foreground]="settings.darkTone() === tone"
+                    [class.text-muted-foreground]="settings.darkTone() !== tone"
+                  >
+                    {{ tone }}
+                  </button>
+                }
+              </div>
+            </div>
+          }
+
           <div class="mt-2.5 flex items-center justify-between gap-2">
             <span class="text-xs text-muted-foreground">Accent</span>
             <div class="flex items-center gap-1.5">
@@ -322,6 +342,7 @@ export class TabBar {
   readonly settingsOpen = signal(false);
   readonly isMacChrome = IS_MAC_CHROME;
   readonly themes = THEMES;
+  readonly darkTones = DARK_TONES;
   readonly accents = ACCENTS;
   readonly iconColorModes = ICON_COLOR_MODES;
   readonly speedUnits = SPEED_UNITS;