Migrate fomantic search and modal CSS to first-party modules (#36869)

Replace the fomantic search.css (520 lines) and modal.css (698 lines)
with minimal first-party modules containing only the rules actually
used. Hardcoded colors are replaced with theme variables, and the
base.css overrides are merged directly into the new modules.

With this change, all original Fomantic CSS is now gone.

**search.css**: 520 → 85 lines
**modal.css**: 698 → 329 lines

Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>

web_src/css/base.css

@@ -34,7 +34,7 @@
   --transition-hover-fade: opacity 0.2s ease; /* fade transition for elements that show on hover */
 
   /* z-index */
-  --z-index-modal: 1001; /* modal dialog, hard-coded from Fomantic modal.css */
+  --z-index-modal: 1001; /* modal dialog */
   --z-index-toast: 1002; /* should be larger than modal */
 
   --font-size-label: 12px; /* font size of individual labels */
@@ -337,37 +337,6 @@ a.label,
   background: currentcolor;
 }
 
-.ui.search > .results {
-  background: var(--color-body);
-  border-color: var(--color-secondary);
-  overflow-wrap: anywhere; /* allow text to wrap as fomantic limits this to 18em width */
-}
-
-.ui.search > .results .result {
-  background: var(--color-body);
-  border-color: var(--color-secondary);
-  display: flex;
-  align-items: center;
-}
-
-.ui.search > .results .result .title {
-  color: var(--color-text-dark);
-}
-
-.ui.search > .results .result .description {
-  color: var(--color-text-light-2);
-}
-
-.ui.search > .results .result .image {
-  width: auto;
-  height: auto;
-}
-
-.ui.search > .results .result:hover,
-.ui.category.search > .results .category .result:hover {
-  background: var(--color-hover);
-}
-
 .empty-placeholder {
   display: flex;
   flex-direction: column;