feat(web): add search to Rules page

Filter sections by typing in the search box — matches against both
section titles and content. Shows result count and a "no results"
message. Expand/Collapse All buttons respect the filtered set.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/index.css

@@ -542,12 +542,34 @@ button:disabled {
 }
 
 /* Rules Page */
+.rules-search {
+  width: 100%;
+  padding: var(--spacing-sm) var(--spacing-md);
+  margin-bottom: var(--spacing-sm);
+  border: 1px solid var(--color-border);
+  border-radius: var(--radius);
+  background: var(--color-surface);
+  color: var(--color-text);
+  font-size: 1rem;
+}
+
+.rules-search::placeholder {
+  color: var(--color-text-muted);
+}
+
 .rules-actions {
   display: flex;
+  align-items: center;
   gap: var(--spacing-sm);
   margin-bottom: var(--spacing-md);
 }
 
+.rules-count {
+  font-size: 0.85rem;
+  color: var(--color-text-muted);
+  margin-left: auto;
+}
+
 .rules-sections {
   display: flex;
   flex-direction: column;