Make disabled SearchSelect read as one element

The disabled widget showed two clashing surfaces in dark mode: the wrapper
(faded via has-[:disabled]) plus the inner search input, which picked up the
global disabled-input fill from common/input.css
(`form input:disabled { background: neutral-secondary-strong }`). That rule is
unlayered, so it beat any utility override on the input.

Exclude the SearchSelect's inner search box from that global rule
(`:not([data-search-select-search])`) so it stays transparent — the wrapper is
then the single faded surface. Standalone inputs (e.g. the Name field) keep
their distinct disabled surface, unchanged.

e2e: assert the disabled inner input computes transparent background (one
element), alongside the existing wrapper-opacity check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

games/static/base.css

@@ -4400,7 +4400,7 @@
     border-left-color: var(--color-slate-500);
   }
 }
-form input:disabled, select:disabled, textarea:disabled {
+form input:disabled:not([data-search-select-search]), select:disabled, textarea:disabled {
   cursor: not-allowed;
   background-color: var(--color-neutral-secondary-strong);
   color: var(--color-fg-disabled);