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>

docs/gotchas.md

@@ -20,8 +20,9 @@ touching the adjacent code.
   `[class.shadow-[...]]` (brackets) does NOT parse — use `[style.box-shadow]`.
   Static class attributes may use arbitrary values freely.
 - Functions called from templates ARE reactive: signals read inside them
-  register on the view's consumer (call-stack-based tracking). That's why
-  `iconClass(entry)` reacting to `settings.iconColors()` works.
+  register on the view's consumer (call-stack-based tracking). That's why a
+  template calling `i18n.t()` re-renders on a language switch — `t()` reads
+  the `locale` signal.
 - Dedicated tools > shell: IDE diagnostics between paired template/class
   edits are often stale mid-sequence — trust `bun run build:ui` (full AOT
   type-check), not the first red squiggle.