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/core/file-icons.ts

@@ -1,4 +1,4 @@
-// File-list glyphs + per-category colors ("Multi" icon mode). Category colors
+// File-list glyphs + per-category colors. Category colors
 // are fixed tokens (never follow the accent) so a folder is always folder-blue.
 // Only the icon glyph is colored; row text stays neutral. Docs and unknown
 // files stay muted on purpose — sparing color is what keeps it scannable.
@@ -8,7 +8,6 @@ type Category = 'image' | 'audio' | 'video' | 'archive' | 'code' | 'doc';
 
 // Class strings are literals so the Tailwind scanner picks them up.
 const MUTED = 'shrink-0 text-muted-foreground';
-const PRIMARY = 'shrink-0 text-primary';
 const FOLDER = 'shrink-0 text-icon-folder';
 const LINK = 'shrink-0 text-icon-link';
 
@@ -85,18 +84,15 @@ export function fileKindKey(entry: FileEntry): string {
   return category ? KIND_KEYS[category] : 'file';
 }
 
-export function fileGlyph(entry: FileEntry, multi: boolean): string {
+export function fileGlyph(entry: FileEntry): string {
   if (entry.name === '..') return 'mynaArrowUp';
   if (entry.type === 'dir') return 'mynaFolder';
-  if (!multi) return 'mynaFile';
   if (entry.type === 'symlink') return 'mynaLink';
   const category = categoryOf(entry.name);
   return category ? CATEGORIES[category].glyph : 'mynaFile';
 }
 
-export function fileIconClass(entry: FileEntry, multi: boolean): string {
-  // plain mode: exactly the pre-color look ('..' has type 'dir' -> primary)
-  if (!multi) return entry.type === 'dir' ? PRIMARY : MUTED;
+export function fileIconClass(entry: FileEntry): string {
   if (entry.name === '..') return MUTED;
   if (entry.type === 'dir') return FOLDER;
   if (entry.type === 'symlink') return LINK;