perf(parcel-sync): use useDeferredValue for UAT search input

React's useDeferredValue lets the input update immediately while
deferring the expensive filter (3186 items) to a lower priority.
Removes the setTimeout debounce in favor of React's built-in
concurrent rendering scheduler. Input stays responsive.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/modules/parcel-sync/components/parcel-sync-module.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useState, useEffect, useCallback, useMemo, useRef } from "react";
+import { useState, useEffect, useCallback, useMemo, useRef, useDeferredValue } from "react";
 import {
   Search,
   Download,
@@ -615,16 +615,17 @@ export function ParcelSyncModule() {
   /*  UAT autocomplete filter                                     */
   /* ════════════════════════════════════════════════════════════ */
 
+  // useDeferredValue lets React prioritize the input update over the filter
+  const deferredUatQuery = useDeferredValue(uatQuery);
+
   useEffect(() => {
-    const raw = uatQuery.trim();
+    const raw = deferredUatQuery.trim();
     if (raw.length < 2) {
       setUatResults([]);
       return;
     }
-    const timer = setTimeout(() => {
     const isDigit = /^\d+$/.test(raw);
     const query = normalizeText(raw);
-      // Filter and sort: UAT name matches first, then county-only matches
     const nameMatches: typeof uatData = [];
     const countyOnlyMatches: typeof uatData = [];
 
@@ -640,12 +641,9 @@ export function ParcelSyncModule() {
       }
     }
 
-      // UAT name matches first (priority), then county-only matches
     const results = [...nameMatches, ...countyOnlyMatches].slice(0, 12);
     setUatResults(results);
-    }, 150);
-    return () => clearTimeout(timer);
-  }, [uatQuery, uatData]);
+  }, [deferredUatQuery, uatData]);
 
   /* ════════════════════════════════════════════════════════════ */
   /*  Auto-connect: trigger on first UAT keystroke                 */