chore: code cleanup - remove duplicates and add caching

- Delete duplicate getCacheStats() function in cache.service.js
- Fix date calculation bug in lotw.service.js (was Date.now()-Date.now())
- Extract duplicate helper functions (yieldToEventLoop, getQSOKey) to sync-helpers.js
- Cache award definitions in memory to avoid repeated file I/O
- Delete unused parseDCLJSONResponse() function
- Remove unused imports (getPerformanceSummary, resetPerformanceMetrics)
- Auto-discover award JSON files instead of hardcoded list

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

src/backend/services/lotw.service.js

@@ -4,7 +4,8 @@ import { max, sql, eq, and, or, desc, like } from 'drizzle-orm';
 import { updateJobProgress } from './job-queue.service.js';
 import { parseADIF, normalizeBand, normalizeMode } from '../utils/adif-parser.js';
 import { invalidateUserCache, getCachedStats, setCachedStats, invalidateStatsCache } from './cache.service.js';
-import { trackQueryPerformance, getPerformanceSummary, resetPerformanceMetrics } from './performance.service.js';
+import { trackQueryPerformance } from './performance.service.js';
+import { yieldToEventLoop, getQSOKey } from '../utils/sync-helpers.js';
 
 /**
  * LoTW (Logbook of the World) Service
@@ -81,6 +82,7 @@ const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));
  * Fetch QSOs from LoTW with retry support
  */
 async function fetchQSOsFromLoTW(lotwUsername, lotwPassword, sinceDate = null) {
+  const startTime = Date.now();
   const url = 'https://lotw.arrl.org/lotwuser/lotwreport.adi';
 
   const params = new URLSearchParams({
@@ -176,7 +178,7 @@ async function fetchQSOsFromLoTW(lotwUsername, lotwPassword, sinceDate = null) {
     }
   }
 
-  const totalTime = Math.round((Date.now() - Date.now()) / 1000);
+  const totalTime = Math.round((Date.now() - startTime) / 1000);
   return {
     error: `LoTW sync failed: Report not ready after ${MAX_RETRIES} attempts (${totalTime}s). LoTW may be experiencing high load. Please try again later.`
   };
@@ -210,21 +212,6 @@ function convertQSODatabaseFormat(adifQSO, userId) {
   };
 }
 
-/**
- * Yield to event loop to allow other requests to be processed
- * This prevents blocking the server during long-running sync operations
- */
-function yieldToEventLoop() {
-  return new Promise(resolve => setImmediate(resolve));
-}
-
-/**
- * Get QSO key for duplicate detection
- */
-function getQSOKey(qso) {
-  return `${qso.callsign}|${qso.qsoDate}|${qso.timeOn}|${qso.band}|${qso.mode}`;
-}
-
 /**
  * Sync QSOs from LoTW to database (optimized with batch operations)
  * @param {number} userId - User ID