Rename the darker tone to AMOLED; file icons are always colored

- Tone: the "darker" option is labelled "AMOLED" in all 7 locales — it is
  the true-black AMOLED palette. The persisted value stays "darker", so no
  settings migration.
- File icons: the Plain/Multi option is gone and the per-category glyphs +
  colors are always on. Removed the iconColors setting (type, default,
  signal, setter, options row, strings) and the plain branch in
  file-icons.ts. A stale "iconColors" key in settings.json is carried
  harmlessly and dropped on the next save.

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

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

@@ -30,7 +30,6 @@ const SPEED_UNITS = [
   { value: 'MBps', label: 'MB/s' },
   { value: 'Mbps', label: 'Mbps' },
 ] as const;
-const ICON_COLOR_MODES = ['plain', 'multi'] as const;
 const TRANSFER_MODES = ['single', 'multi'] as const;
 const CONCURRENCY_CHOICES = [2, 3, 4, 6, 8] as const;
 
@@ -242,23 +241,6 @@ const CONCURRENCY_CHOICES = [2, 3, 4, 6, 8] as const;
             </div>
           </div>
 
-          <div class="mt-2.5 flex items-center justify-between gap-2">
-            <span class="text-xs text-muted-foreground">{{ i18n.t('options.fileIcons.label') }}</span>
-            <div class="flex rounded-md border border-border p-0.5">
-              @for (mode of iconColorModes; track mode) {
-                <button
-                  (click)="settings.setIconColors(mode)"
-                  class="rounded px-2 py-0.5 text-[0.6875rem]"
-                  [class.bg-accent]="settings.iconColors() === mode"
-                  [class.text-foreground]="settings.iconColors() === mode"
-                  [class.text-muted-foreground]="settings.iconColors() !== mode"
-                >
-                  {{ i18n.t('options.fileIcons.' + mode) }}
-                </button>
-              }
-            </div>
-          </div>
-
           <!-- Interface scale: a continuous stepper, 50%..400% in 10-point
                steps. One lever moves the whole UI (root font-size; everything
                is rem), which is also why this popover itself grows with it. -->
@@ -463,7 +445,6 @@ export class TabBar {
   readonly themes = THEMES;
   readonly darkTones = DARK_TONES;
   readonly accents = ACCENTS;
-  readonly iconColorModes = ICON_COLOR_MODES;
   readonly speedUnits = SPEED_UNITS;
   /** "100%" for the stepper readout; the value itself lives in settings. */
   readonly scalePercent = computed(() => `${Math.round(this.settings.uiScale() * 100)}%`);