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>

common/input.css

@@ -127,11 +127,14 @@
   }
 }
 
-form input:disabled,
+/* Standalone form controls get a distinct disabled surface. The SearchSelect's
+   inner search box is excluded: it's a composite widget that owns its disabled
+   look on the wrapper (has-[:disabled] in _CONTAINER_CLASS), so painting the
+   inner input here would render a nested box inside the wrapper. */
+form input:disabled:not([data-search-select-search]),
 select:disabled,
 textarea:disabled {
   @apply cursor-not-allowed bg-neutral-secondary-strong text-fg-disabled;
-   
 }
 
 .errorlist {